Having first aired on October 5, 1999, Angel was an attempt to tell a more mature story than its parent show, Buffy the Vampire Slayer. While its ambitions meant that it never quite gained the popularity of Buffy, it did manage to evolve some of the central storytelling techniques that Buffy had pioneered.
Instead of having one big bad who moved the plot forward each season, Angel did something different. The show had an overarching entity face off against Angel Investigations throughout the show's run, with other villains coming in and out to cause complications for both parties. This juggling of storylines didn't always succeed, but it did manage to produce several iconic villains.
Angelus
Originally the big bad of Buffy season 2, the sadistic and soulless version of Angel returned during Angel’s 4th season when the group needed his expertise to take down The Beast. While Angel Investigations succeeded in their efforts, Angelus went on to hunt everyone in the Hyperion, only to be taken out by Faith and her slayer blood.
Angelus was a truly menacing presence not just because of his cruelty but due to the audience's familiarity with him as the otherwise kind protagonist Angel. It's because of this duality that he was such a threat on the show, despite only starring in 3 episodes of Angel (not counting flashbacks).
Marcus Hamilton
Introduced during the show’s 5th season, Marcus Hamilton acted as the half-demon enforcer of the Wolfram & Hart law firm. In this capacity, he kept an eye on Angel’s shenanigans and eventually caught wind of his plan to take out the Circle of the Black Thorn.
Though he was largely ineffective in stopping Angel from toppling Wolfram & Hart's Los Angeles division, Marcus Hamilton still proved to be a thorn in Angel’s side. He was the final opponent Angel had to fight on screen, and kept the vampire on his toes thanks to the power of Wolfram & Hart flowing through his veins.
The Beast
The most physically imposing villain Angel Investigations fought, The Beast acted as an agent for Jasmine and carried out her plans to bring about the apocalypse. Though this essentially meant he was a lackey, this didn’t make him any less threatening, however, as he was able to black out the sun and take out all of Wolfram & Hart on his own.
Because of the Beast’s raw power, Angel Investigations had to bring in the slayer Faith to help defeat the demon. She was little match for the Beast, but was able to distract the demon long enough for Angelus to stab him with a magical dagger. An abrupt farewell, but one that was fitting for the character.
Sahjan
A non-corporeal demon with the power to travel through time, Sahjan first made himself known in the show's third season when he brought Holtz to the 21st century to kill Angel. Unbeknownst to Holtz and everyone else, however, Sahjan's true goal was to eliminate Angel's son, Connor, who was prophesized to kill Sahjan.
Though Sahjan's plans don't exactly hold up under close investigation, the demon still makes for a menacing shadow figure, willing to alter prophecies and work with Wolfram & Hart to get his way. Perhaps the best aspect of Sahjan, however, is his dry and sarcastic sense of humor, something many Angel villains lacked.
Jasmine
The mysterious entity possessing Cordelia and controlling the Beast, Jasmine was a rogue member of the Powers That Be who planned to bring about world peace by eliminating free will. To do this, she played the long game by manipulating events from her own dimension until the time came for her to be born on Earth.
Though the decision to make Jasmine the force behind Angel’s previous storylines was unpopular, her overall goal was unique for the series. She saw herself as the hero of her story, more than any other villain, and Gina Torres sold her conviction effortlessly.
Lindsey McDonald
Perhaps the most complex character in the entire Buffyverse, Lindsey McDonald is a lawyer for Wolfram & Hart who develops a vendetta against Angel and hires several demons and assassins to kill the vampire, including the rogue slayer Faith. This hasn't stopped Lindsey from working with his nemesis on several occasions though, such as when Wolfram & Hart were set to assassinate three children.
What makes Lindsey such a complicated person is that he has rigid moral convictions despite working for Wolfram & Hart. It ultimately led to his departure from the show as a seemingly changed man, yet his disdain for Angel brought him back to L.A. for the show's final season. His return showed that not all redemptive arcs stick, something which is true of real life.
Daniel Holtz
The Big Bad of Angel’s third season, Holtz was a vampire hunter from the 1700s whose family had been murdered by Angelus and Darla. Brought to the 21st century by Sahjan, he jumped back into hunting Angel without hesitation, going so far as to steal his child just to hurt the vampire.
Equal parts sympathetic and menacing, Holtz worked as a villain because he was able to change his plans to meet his overall goal. His mission to kill Angel quickly became one of enacting justice through torment, and he succeeded in the end given that his death resulted in Connor dumping Angel into the ocean.
Darla
The vampire who sired Angel, Darla was originally a minor character killed off in Buffy's first season before being brought back by Wolfram & Hart to torment her former lover. It was in this role that she truly began to shine as a character.
During Angel's second season, she appeared in his dreams and sapped his strength before making him question reality when she met him in person. Though her sway wasn't enough to turn Angel evil, she did manage to break his faith in humanity, something no other villain could pull off.
Lilah Morgan
The face of Wolfram & Hart during the show’s third season, Lilah Morgan is a conniving lawyer who happens to be the show’s most strategic thinker and underhanded manipulator. She might not always win every battle against Angel Investigations, but her track record is better than most, especially considering how she worked her way up to head of special projects.
Even as she was given more humanity in episodes like “Billy,” she never went through a redemptive arc like her co-worker Lindsay McDonald. It goes to show her as being a nuanced character without taking away from her status as a threat.
Wolfram & Hart
Perhaps a cheat considering they’re a collective rather than an individual, Wolfram & Hart is nevertheless the most frequent nemesis Angel and his friends face throughout the series. They’re the group behind most of the evil Angel Investigations faces and are always looking to control the vampire through their actions.
Because of their omnipresence in the series, they’re not just Angel’s main enemy, but also the show’s most thematically important one. As a faceless law firm, they represent the evil that the show chooses to fight, the kind that can never be wiped away.