Riley Finn is a fictional character created by Joss Whedon for the television series Buffy the Vampire Slayer. Portrayed by Marc Blucas, Riley was introduced in the 1999 season 4 premiere episode, "The Freshman", and Blucas was part of the series credited cast for the second part of season 4 and the first part of season 5. Most notably, Riley is one of three long-term romantic interests for series' heroine Buffy Summers (Sarah Michelle Gellar).

Whedon intended Riley to be the antithesis of Buffy's boyfriend of the past three seasons, Angel (David Boreanaz), who now headed his own spin-off show. In stark contrast to broody, often pensive Angel, Riley is optimistic, trustworthy and reliable, and in theory presents Buffy with her first opportunity for a "normal" romantic relationship. However, Riley also leads a double life: he is both teaching assistant at UC Sunnydale and a member of The Initiative, a government-sponsored special operations team which both researches and combats the demons which roam Sunnydale. This allows him to interact with Buffy both in her civilian life and assist her with her duties as a Slayer; while Buffy has supernatural powers associated with her role, Riley must rely instead on his extensive military training.

In the show's fifth season, writers experimented with making Riley a more complex character, and so depicted Riley beginning to "fray around the edges". This storyline culminated in Riley being written out of the series in 2000. In 2002, Blucas returned for a final televised appearance in the show's sixth season, where he is seen to have moved on from Buffy and married. Subsequently, the character appears in Expanded Universe material such as the canonical comic book continuation to the series, Buffy the Vampire Slayer Season Eight (2007–11). In Season Eight, the precise nature of Riley's role in the storyline is unclear for much of the story; writer Jane Espenson, however, wrote a Riley one-shot comic book focusing on Riley and his wife.

A native of Huxley, Iowa, Riley is Buffy Summers' boyfriend for parts of seasons four and five. He is first introduced as Professor Walsh's TA in a psych class Buffy and Willow are in. Riley realizes his feelings for Buffy after punching Parker Abrahams for an inappropriate comment Parker makes regarding their night together. Even though he leads a double life as part of a secret government organization known as The Initiative, Buffy finds some normalcy in Riley as a regular college guy and someone to whom she could relate. Initially, each keeps the other from knowing their respective secret lives, but the truth comes out during the events in the Emmy-nominated episode "Hush".

Buffy and Riley fight demons together and continue saving each other's lives and the world, although Riley is never quite let into Buffy's inner circle. Initially, Riley automatically assumes that all demons are evil, but discovers that demons are capable of both good and evil just as humans are after assisting in saving Oz from the Initiative complex. Having been torn between the Scooby Gang and the Initiative for some time, Riley decides to leave the Initiative upon discovering the extent of its corruption, and spends the remainder of the season in hiding within the ruins of Sunnydale High.

The Initiative was destroyed at the end of season 4, and Riley is relieved of his military standing. He is left at loose ends, and his behavior becomes reckless. Over time, Riley begins to see himself as below Buffy in strength, and begins to push his body well past its limits. In "Out of My Mind", it is discovered that the drugs that Professor Walsh had secretly fed him are causing Riley's pain receptors to shut down and his heartbeat to spike, and could eventually have killed him. Even with this knowledge, Riley initially refuses to accept medical treatment from the government out of paranoia, though Buffy eventually convinces him to do so. Rendered a normal human by the procedure, Riley's insecurities and feelings of weakness only increase, and he becomes increasingly frustrated with Buffy's seeming inability to open up to and be honest with him.

Seeking thrills, and wondering what Buffy seems to find so appealing about vampires – Buffy having allowed both Angel and Dracula to drink from her – Riley begins to let vampires feed from him, which Buffy discovers in the episode "Into the Woods" when Spike reveals Riley at the vampire's nest. His behavior, as well as Spike's manipulations and a sense that Buffy would never truly love him, lead to their breakup. Riley leaves Sunnydale to join another black ops army unit fighting demons elsewhere.

Riley returns in the season 6 episode "As You Were", in which he shows up unexpectedly with his new wife, fellow demon hunter Sam (Ivana Miličević), tracking a demon about to hatch eggs that could wipe out Sunnydale. When Riley learns that Buffy has been sleeping with Spike, he consoles her on her struggles with her life, and forgives her after she apologizes for what happened between them. The battle done, Riley leaves Sunnydale, never to return again. He is, however, mentioned in the season 7 episode "The Killer in Me" where Buffy attempts to contact him for advice on the malfunctioning chip in Spike's head. Riley then contacts soldiers from the Initiative, who help diagnose Spike's condition and then discuss with Buffy that per Riley's instruction, it is her decision to remove or repair the chip in order to save Spike's life. Buffy has them remove the chip.