Focused on career criminal Raymond “Red” Reddington and FBI agent Elizabeth Keen, NBC’s The Blacklist has kept viewers enthralled through six seasons thus far with its twists, turns, and tumultuous relationship between the two main characters.

But alongside the two central characters is a lengthy list of supporting ones that make the series as riveting as it is. These range from characters that appear in every episode, to a few that show up sparingly, but always make their mark when they do.

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Who are these characters? There are many, but here are the 10 best. Most are living, some are now dead, but all, at one point of another, are or were part of Raymond’s incredibly massive network.

Harold Cooper

Harold in The Blacklist

A main character on the series, Harold has been a huge part of every storyline.

As the Assistant Director for Counter-terrorism at the FBI, he’s the head honcho and the man the entire team goes to when they need clearance to get something done. But they also go to him for advice and know they can trust him with anything. Harold is like a surrogate father to Liz.

And while he has morals coming out the wazoo, Harold still struggles with his desire to protect his team, and even Raymond. He even went so far as to literally save Raymond’s life. Anyone would be lucky to have a boss like Harold.

Dembe Zuma

Dembe

Fiercely loyal to Raymond, Dembe is his right-hand man and bodyguard. But he’s far more than that. He’s his best friend, his confidant, and his moral compass, even when Raymond refuses to listen to Dembe’s always prophetic and wise words.

Dembe will do whatever it takes to help Raymond, even put his life on the line. But when put in a difficult situation where he had to make a choice between protecting Raymond and protecting Liz, it put a wrench in his relationship with Raymond. Dembe had a crisis of faith and decided to quit. But we doubt this is the last we’ll see of him.

Aram Mojtabai

Aram in The Blacklist

In any series that deals with terrorism, the FBI, CIA, or any type of cyber-attack, the “IT guy” or “IT gal” never gets the attention he or she deserves. Yet this person is often the one who saves the team in the nick of time through their savvy computer and networking skills.

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In The Blacklist, this is Aram. As the Strategic and Tactical Technician, he isn’t as skilled with a gun and hand-to-hand combat like the rest of the team. But put him in front of a computer, smartphone, or other electronic device, and he will find the person or thing you’re looking for, stop a bomb from detonating, or curb a massive attack in minutes.

Tom Keen

Tom argues with Red in The Blacklist

No longer on the series having sadly been killed, later appearing on the short-lived spin-off series The Blacklist: Redemption,  Tom was Liz’s husband, a supposed schoolteacher who turned out to actually be a man named Christopher Hargrave who was kidnapped as a child. He turned to thievery as a teen and was recruited by Raymond to keep an eye on Elizabeth. But they ended up falling in love, at which point Red fired him.

Tom kept up the façade, marrying Liz until she finally figured out his true identity. Surprisingly, they remained together (after trying to kill one another!) and, in a weird twist, began to work together to figure out Raymond’s true identity, too.

Mr. Kaplan

Mr. Kaplan in The Blacklist

Real name Kathryn Nemec, Mr. Kaplan, as she’s called by her associates (yes, she) was Raymond’s fixer and cleaner. After a murder or unfortunate accident, one call to Mr. Kaplan and you know it will be taken care of with little trace of what had happened left for anyone to ever find.

Initially nanny to Liz as a baby, Mr. Kaplan honed her skills for cutting up and disposing of bodies while working at a morgue.

Her work for Raymond was her downfall: she was the only one who knew where all of the bodies were hidden because, well, she put them there. In the end, her desire, like Dembe, to protect Liz and reveal Raymond’s big secret led to his assassination attempt on her, and later her own suicide.

Glen Carter

Blacklist Glen

Providing much of the series’ comic relief, Glen is a lowly administrator at the DMV, but also a skip tracer thanks to the access he gains through his regular employment.

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Another name in Raymond’s Rolodex who he frequently calls upon, Glen is crass and irritating, but it’s obvious that Raymond has a soft spot for him.

Constantly eating and cracking jokes, he always pulls out the information that Red needs, even if it’s sometimes like pulling teeth to get it.

Alexander Kirk

Constantin_Rostov blacklist

Real name Constantin Rostov, Alexander is a former KGB agent and Elizabeth’s stepfather.

Now a Russian billionaire with tremendous connections to various criminal enterprises, he went toe-to-toe with Raymond, seemingly following a long history of rivalry between the two, making for one of the more interesting storylines of the series. Viewers were biting their lips trying to figure out who really is Liz’s daddy?

Suffering from a rare genetic blood disorder, Alexander sought out Liz and baby Agnes, believing they could provide him with stem cells for a cure. But he didn’t realize, and was devastated to find out, that Liz is not his biological daughter.

His whereabouts are currently unknown. But without the stem cells, he might already be dead.

Teddy Brimley

A close up of Teddy Brimley with his oxygen tube on The Blacklist.

Another member of Red’s trusted team, Teddy is a skilled interrogator who calmly closes the door, rolling his oxygen tank behind him, to do his dirty work. And he always gets Red the answers he needs from an unwillingly participant.

Not averse to using unconventional torture methods, Teddy will bring out exotic snakes, rats, or a menacing toolkit that has the person in his custody squirming before he even begins his process.

Suffering from various conditions including hypoxemia, congestive heart failure, diabetes, and asthma, none of his ailments slow Teddy down. He’s just as terrifying as any professional interrogator with a clean bill of health.

Katarina Rostova

Revealed to be Liz’s real mother, and apparently still alive, Katarina Rostova has a storied and confusing back story. A former KGB agent, she was assigned to seduce and spy on Raymond Reddington, but began working as a double agent.

The supposed death of the “real” Raymond Reddington, and the story of how the man who now claims to be Raymond Reddington took on his identity, all trace back to Katarina.

Even though she’s only been seen sparingly in the series, Katarina is a major part of the story, and we’ll likely be seeing more of her in the upcoming seventh season.

Ilya Koslov

Believed to be the true identity of Raymond Reddington before having plastic surgery to take on that person’s face, Ilya only appeared in a single episode thus far. But if what we’re led to believe his true, Ilya is not only a supporting character, but effectively the main character of the series.

A childhood friend of Katarina, who was hopelessly in love with her, Ilya supposedly used one of Red’s many connections, a skilled plastic surgeon, to take on the identity of the real Red. And he seemingly fell right into Red’s criminal ways, building the enterprise while trying to protect the love of his life and her now-grown daughter.

Of course the show likes to deliver many twists and turns. But we’re sure to find out more about Ilya, Raymond Reddington, and how the two are connected, in the upcoming season.

NEXT: The Blacklist: 10 Best Characters, Ranked