The world of Hollywood is a fickle one. It's a world where today's unknowns can become tomorrow's brightest stars, and where today's biggest names can become tomorrow's cautionary tales. There's no rhyme or reason for who makes it big and who never succeeds in the long run.

When it comes to the ever-expanding cast of Grey's Anatomy, it really does seem totally random and hit or miss when you look at who's made it to the A-list and whose career sadly never took off.

There's no logic of career longevity behind any part of it, as not every member of the original cast has maintained increasing levels of success. However, not every fresh face makes it big, either, often instead retreating to the obscurity from which they briefly emerged into the halls of Grey Sloan Memorial Hospital.

Then again, Hollywood is truly fickle. Just because certain Grey's stars have worked their way up to the A-list so far, that doesn't mean they can't tumble from their lofty positions at any time.

Also, even if certain cast members have yet to make it big, they're really just one standout role away from changing it all.

With that said, here are 10 Grey’s Anatomy Stars Who Became A-Listers (And 5 Whose Careers Flopped).

A-List: Sara Ramirez

Callie looks angry at Arizona in Grey's Anatomy

From season two through season twelve, Sara Ramirez starred on Grey's as orthopedic surgeon Calliope "Callie" Torres. Whip smart and unabashedly confident, Callie, through Ramirez's portrayal, transcended from the unenviable position of romantic road block to fully formed and inspirational heroine.

Through Callie's narrative significance, Ramirez began to make a stronger name for herself within the world as well.

Ramirez became a staunch supporter of LGBTQ rights, even receiving an ally award from the Human Rights Campaign for her efforts toward promoting equality -- a distinction that predated her decision to come out as bisexual in 2016.

In addition to her work on the small screen, Ramirez has received a Tony Award and an Outer Critics Circle Award for her theatre career, and has released a self-titled EP as well.

A-List: Jeffrey Dean Morgan

Denny Duquette is a perfect example of a character who over-stayed their welcome and left a sour taste in many fans' mouths as a result of it.

Previously a sad, lovable character with a bittersweet ending, Denny's duration on the series was over-extended through cringe-worthy plot device after plot device.

If one successful thing came from Denny's duration on the series, however, it was undoubtedly providing a launching pad for Jeffrey Dean Morgan's future career.

In addition to his time as Izzie's ill-fated love on Grey's, Morgan has also recurred on cult hit Supernatural and starred in countless genre movies, such as Watchmen and Batman v Superman.

However, above all else, Morgan is now undeniably most well-known for his bone-chilling turn as the sociopathic Negan on the long-running horror series The Walking Dead.

Flopped: Brooke Smith

Brooke Smith Greys Anatomy

Some characters just never seem to find their places within an extremely large and talented ensemble. Unfortunately for Brooke Smith, her Dr. Erica Hahn was one who stuck out like a sore thumb from her very introduction.

Extremely tightly wound and competitive, Hahn had a chip on her shoulder from the get go, one that made it difficult to connect with her character even as the connected romantically with the more likable Callie.

Since Hahn's unceremonious departure from Grey's at the start of its fifth season, Smith's career hasn't quite had the upward trajectory that some of her fellow departed cast mates have had.

She would go on to have small, recurring roles in series such as Bates Motel, Ray Donovan, and Bosch, but never a main role of any sort. Similarly, she had a minor role in the popular movie Interstellar.

A-List: Sandra Oh

Yang in Grey's Anatomy

Arguably one of Grey's most inspiring characters to date, cardiothoracic surgeon Cristina Yang presented the perfect role model for girls everywhere who refused to let anything stand in the way of achieving their dreams.

Cristina was truly uncompromising, brave, and brilliant, and Sandra Oh's departure from the series after season 10 presented one of the show's biggest losses to date, one that certain groups of fans believe it has yet to rebound from.

Since starring on Grey's, Oh has had a considerable amount of successful work elsewhere as well.

She had starring roles in the anthology series Thorne and American Crime, and is starring in the forthcoming drama series Killing Eve.

As a result of her time on Grey's, she was also nominated for countless Golden Globes, Screen Actors Guild Awards, Emmys, and Satellite Awards.

A-List: Jesse Williams

Jesse Williams in Grey's Anatomy

Introduced in season six of Grey's, Jackson Avery is one of the show's many characters struggling to distance himself from his lineage. Determined to get by on his own merits, and not the merits of those that came before him, he works his way up to the top of the hospital's plastic surgery division.

In addition to his acting career, Jesse Williams has established himself as a noteworthy figures in other fields, such as modeling, and political activism.

He has also appeared in music videos for artists including Rihanna and Demi Lovato.

Williams is also a passionate activist, sitting on the board for the advocacy group The Advancement Project and writing numerous op-eds on racism, injustice, and diversity for publications such as CNN and The Huffington Post.

Flopped: Melissa George

Melissa George Greys Anatomy

For eight episodes during season five of Grey's, Melissa George appeared as Sadie Harris, a surgical intern with less than reputable credentials.

Her character was reconceived of multiple times during the writing process, having once meant to be a queer character involved with Hahn and Callie in some capacity. Ultimately, her character proved a poor fit for the show, and was needed to be seen as unfit and undeserving of being within the program.

Prior to the polarizing role on Grey's, Melissa George had already had her fair share of dealing with fan backlash for her turn as the nefarious Lauren Reed on fellow ABC series, Alias.

After departing Grey's, her career has been filled with short stints on successful shows, such as The Good Wife, or leading roles on shows that were never able to succeed, such as The Slap or Heartbeat.

A-List: Kate Walsh

Addison Montgomery was one of Grey's most divisive characters from the very beginning -- especially seeing as she stood in the way of the series' central love story of Meredith and Derek.

However, no amount of divisiveness would deter Addison from being exactly who she was, even earning the character her own long-running spin-off series, Private Practice.

Thanks to the strength of Kate Walsh's performance, Addison was allowed the time and space to develop into a truly sympathetic character.

 Also, thanks to her work as Addison for all those years, Walsh has gone on to have quite the successful career.

She starred in the short-lived series Bad Judge, before moving on to star in the wildly popular Netflix series 13 Reasons Why. She has also appeared in successful movies including Girls Trip and The Perks of Being a Wallflower.

A-List: Chris O'Donnell

Finn Dandridge

In seasons two and three of Grey's Anatomy, Chris O'Donnell had the recurring role of Finn Dandridge, also known as McVet, one of Meredith's ill-fated love interests who could just never compare to Derek in any way.

There was nothing particularly wrong with McVet, but there was also nothing particularly compelling about him either.

His character primarily existed as a temporary speed bump within the good 'ship MerDer's journey, so it's no surprise that, following his and Meredith's separation, he was never heard from again.

Since appearing as Finn for nine episodes across Grey's second and third seasons, Chris O'Donnell has gone on to have much more success in the television world.

Ever since 2009, O'Donnell has starred on the NCIS offshoot, NCIS: Los Angeles, in the leading role of G. Callen, the lead special agent for the series' NCIS office.

Flopped: T.R. Knight

TR Knight Greys Anatomy

George O'Malley was one of Grey's most lovable characters from the very beginning, eternally awkward and kind.

His tragic death in the show's fifth season finale/sixth season premiere represented the show's first big loss, showing just what the series would be capable of doing to even its most beloved characters in the many, many years to come.

No matter how lovable George may have been, and how well-received T.R. Knight's portrayal was, which brought him multiple award nominations, Knight's career post-Grey's hasn't measured up to his success during his Grey's tenure.

He's made appearances of different recurring capacity on shows such as Law & Order: SVU, The Good Wife, The Catch, and When We Rise. He has also appeared in various theatrical roles on and off-Broadway.

However, nothing has matched the success brought to him by his time as George.

A-List: Rachael Taylor

Trish recording a podcast in Jessica Jones

In season seven of Grey's, Lucy Fields served as an attendant for Callie's pregnancy, and also would go on to have a brief, yet incredibly complicated romantic relationship with Dr. Alex Karev. Her character would exit the series when she decided to take a job opportunity at the Namboze Clinic in Malawi.

Lucy was never an especially crucial character, nor was she a very popular one. However, since Rachael Taylor's time on the long-running medical series came to an end, her career has only been on an upward trajectory.

She had a few short-lived series under her belt, such as an unsuccessful Charlie's Angels reboot at ABC in 2011, but since 2015, Taylor has been starring in Netflix's Marvel properties as Patricia "Trish" Walker, the future Hellcat of Marvel comics fame.

A-List: Chyler Leigh

Chyler Leigh as Dr Lexie Grey in Grey's Anatomy

Grey's Anatomy may have been all about Meredith Grey to begin with, but it was her younger half-sister, Lexie Grey, who truly stole the hearts of much of the audience.

Adorably nerdy and smarter than everyone else in the room, Lexie, also known as "Little Grey" and "Lexipedia," brought a much-needed sense of warmth and heart to a series so profoundly based in the world of logic and reason. Lexie's tragic death in the series' eighth season finale remains one of its biggest mistakes to this date.

However, in taking Lexie off, the show did, at least, allow the world to experience so much more of Chyler Leigh's incredible talents in other forms.

Since 2015, Leigh has starred as Alex Danvers on the CBS/CW series Supergirl, a role that has earned her considerable praise and accolades, particularly for her depiction of an adult coming to terms with her orientation.

Alongside her husband, Nathan West, she also produces music in the band East of Eli.

Flopped: Isaiah Washington

Isaiah Washington on Grey's Anatomy

Preston Burke was hardly ever a fan-favorite character, but there's no denying that he was an important one, especially in regards to his relationship with Cristina Yang.

His departure from Grey's Anatomy was extremely abrupt -- which is, in fact, reported to have been due to behind the scenes issues between Isaiah Washington and T.R. Knight, involving Washington's use of homophobic language in a dispute with Patrick Dempsey.

Washington's departure from Grey's has led to a subsequently quieter career.

Washington himself has noted that he feels as though the acting part of himself was forever changed and destroyed by this experience.

He reprised his role of Preston Burke in Cristina's final episode in the series in 2014, and since 2014, he has been starring on The CW series The 100 as Chancellor Thelonious Jaha.

A-List: Patrick Dempsey

For eleven seasons, Derek Shepherd was the leading man of Grey's Anatomy, a world class neurosurgeon and roguishly handsome bad boy turned everyman with a heart of gold.

As a devoted father and husband, a dedicated friend, and a consummate professional, Derek was everything that the series needed to keep it grounded -- the perfect rational foil to Meredith's dark and twisty lifestyle.

The loss of Derek from the show following its eleventh season has produced a show that is fundamentally different from what it once was. For some, it may be better.

However, for fans from the very beginning, it's hard to even recognize Grey's without Patrick Dempsey's McDreamy stealing the show.

Since starring as Derek, Dempsey has appeared in light-hearted romcoms such as Enchanted and Bridget Jones's Baby. He has also established himself as quite the accomplished racecar driver, and put much of his own money into funding and fundraising for cancer research.

A-List: Ellen Pompeo

Grey's Anatomy Ellen Pompeo as Meredith Grey smiling

What would Grey's Anatomy be without the very woman who gave the show its title?

For fourteen years and counting, Ellen Pompeo has started as the wonderfully dark and twisty Meredith Grey. Meredith has come a long way from the unsure girl we met in the pilot, growing in strength and vulnerability both over the course of fourteen long seasons.

She's gone through a whole hell of a lot in those years, and perhaps more than any other character on the show has, for that matter. However, it's Pompeo's performance that keeps her grounded, never straying too far into the melodramatic to come back.

Pompeo's résumé may not be all that long, but given that it's her shoulders that Grey's rests upon, what else would you expect?

As of 2018, she is the highest paid actress on a television drama, earning $20 million for seasons 15 and 16, and receiving a producer credit for them as well.

Flopped: Katherine Heigl

Katherine Heigl as Dr. Izzie Stevens in Grey's Anatomy

Having starred on Grey's for its first six seasons as one of the show's most polarizing characters to date, Katherine Heigl had a career marked for trouble from the start.

Of course, some of that eventual trouble was self-inflicted, as she publicly declared that she wouldn't submit herself for the 2008-2009 Emmy race due to poor quality material on Grey's.

The drama that followed was legendary, with reports of conflicts between Heigl and Shonda Rhimes leading the way. So when Heigl departed the series during its sixth season, tensions were high and expectations for her career even higher.

Yet, time and again, the audiences have not come out to support her in any of her pursuits. She has starred in unsuccessful works on both the large and small screens, including One for the Money, The Big Wedding, State of Affairs, and Doubt.

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Who do you consider Grey's Anatomy's biggest successes and failures? Let us know in the comments!