52 celebrities you probably forgot were on 'Veronica Mars'

Seyfried portrayed Lily Kane, Veronica's best friend whose murder is the focal point for season one. Veronica spends the entire first season trying to figure out who really murdered Lily. Along the way, other discoveries are made that affect the lives of many people in Neptune.

Ashmore took on the role of Troy Vandegraff, a love-interest of Veronica's who, unbeknownst to her, tried to smuggle steroids from Mexico into the US.

Ashmore appeared on four episodes during the first season, and a fifth on the second.

The "Simple Life" star portrayed Caitlin Ford, an 09er who was dating Logan Echolls while also seeing a member of the PCH Biker Gang in secret. This side-relationship eventually leads to credit card fraud and Caitlin's rejection from the elite group for life.

On this episode, Veronica is asked to track down a classmate's father. She eventually discovers that the father had transitioned into a woman, portrayed by Academy Award-winner Leo.

Pratt appeared as Georgia, a Neptune High School student who was conned out of $6,000. Luckily, Veronica was able to retrieve the money.

Hamlin played Aaron Echolls, an action star with a list of horrific behaviors, like cheating on his wife, physically abusing his son, and beating random people. (In one graphic scene, Aaron is seen whipping his daughter's abusive boyfriend within an inch of his life.)

But his most disgusting action is sleeping with, and then murdering, his son's underage girlfriend, Lily Kane.

Hamlin's character appeared on 12 episodes throughout the first and second season, and was killed off on the season two finale.

Rinna shined as Lynn Echolls, the Echolls family matriarch who turned to alcohol and drugs to cope with the behavior of her abusive and misogynistic husband.

Rinna appeared on two other episodes during the first season, "An Echolls Family Christmas" and "Clash of the Tritons," the latter of which ended with her character committing suicide.

Lynch portrayed Mrs. Donaldson, a teacher who becomes frustrated when Veronica questions the results of a student body election.

The "Zero Dark 30" star played Sarah, a pregnant neighbor who enlists Veronica's help to recover a stolen journal before going missing. Veronica eventually finds Sarah and the diary, which holds a shocking revelation about the father of Sarah's child.

Bennet played Casey Gant, a stereotypical 09er who Veronica and her dad are asked to retrieve from the Moon Calf Collective cult. Upon investigating, however, the two discover that the "cult" is not as harmless as everyone believes.

Bennett would later appear again on episode 21, "A Trip to the Dentist."

The actor had a recurring role as Detective Leo D'Amato, a one-time colleague of Keith Mars and a one-time boyfriend of Veronica.

Greenfield would go on to appear on 10 more episodes throughout the series and reprise his role in the movie. Greenfield also appears on several episodes of the "Veronica Mars" Hulu revival.

Paul took on the role of "The Worm," a man who is wrongfully accused of kidnapping and strangling various young girls throughout Neptune.

Known for his comedic roles, Anderson played Percy "Bone" Hamilton, a record company owner who enlists Veronica and her dad to help find his missing daughter, Yolanda.

Coleman played Gabrielle Pollard, a friend of Yolanda's who offers Veronica some guidance for finding the missing girl.

The "Big Little Lies" actor portrayed Mr. Rooks, a history teacher who's accused — and later found guilty — of sexually assaulting a student.

Meester played Carrie Bishop, the student who initially accused Mr. Rook of sexual assault. It was eventually revealed that Carrie was making the accusation on behalf of her friend who was too scared to come forward.

Meester also appeared on episode 21, "A Trip to the Dentist." Though her character had a major part on the "Veronica Mars" movie, The Hollywood Reporter noted that Meester was unable to reprise her role and was replaced by Andrea Estella.

Although she didn't have as much screen time as Scott and Meester, Lakin appeared in "Mars vs. Mars" as Susan Knight, the student who was actually assaulted by Mr. Rook.

Hannigan made several appearances as Logan's half-sister Trina. Although she was first seen on the 15th episode, she was mentioned on two prior episodes: "Clash of the Tritons" and "Lord of the Bling."

Hannigan would go on to appear on two more episodes: one on the first season and one on the second.

The '90s star played Caz Truman, a basketball player who is described as someone who would "flirt with a trash can if it had boobs."

Bryan also appeared on episode 17, "Kanes and Abel's."

Marino took on the role of Vincent "Vinnie" Van Low, the rivaling private investigator that most viewers loved to hate.

Marino's character would appear on 10 episodes throughout the series, as well as the movie.

The '90s heartthrob returned to TV screens when he was cast as Ben, an Alcohol, Tobacco, Firearms, and Explosives agent who goes undercover at Neptune High School to investigate a string of bomb threats.

The actor took on the role of Norris, a student who's accused of developing plans to plant a bomb in the school.

McMillian played Pete, a classmate who worked with Ben to falsely implicate Norris. His actions, Veronica discovered, were the result of being bullied by Norris in middle school.

Carpenter took on the multi-episode role of Kendall Casablancas, Dick and Cassidy's stepmom who just so happens to hook up with Logan on the side.

But, as the season progressed, Kendall proved she's more than a "dumb trophy wife." In fact, she's a brilliant con artist working with a notorious crime family.

Carpenter's character appeared on 11 episodes through the series before being killed off on the season three premiere.

Thompson played the daughter of a famous baseball player who makes many waves during her time at Neptune High School. She develops a romantic relationship with Wallace, which frustrates Veronica given Jackie's manipulative behavior. Over time, the tension between Veronica and Jackie dissolves and the two become friendly.

Thompson appeared on all 22 episodes of the second season. Her character's storyline ended when she returned to New York City to raise the son she'd left behind.

Goodman provided some humorous lines and, unknowingly, played a role in helping Veronica solve a few side-crimes.

Ritter's character appeared on eight episodes during the second season, as well as the movie.

Known for his comedic roles, Guttenberg switched gears to play the charismatic but sleazy Mayor Woody Goodman. The season revolved around a mysterious bus crash that killed multiple Neptune High Students. As Veronica and Keith dug into the mystery, they eventually discovered that Woody is a serial child molester and many of his victims were killed in the crash.

Guttenberg appeared on eight episodes throughout the series.

The "Sopranos" alum played Jessie Doyle, a Neptune High School student whose father was driving the bus that crashed and led to the death of several students. Doyle enlisted Veronica's help to prove that her father didn't intentionally crash the bus. Veronica was able to prove the man's innocence but, in the process, discovered he was having an affair.

Smith's character unknowingly gave Veronica some insight that would help her prove the bus driver didn't cause the crash.

Williams, whose credits also include "Friday Night Lights," took on the role of Nathan Woods. At first, viewers believe Nathan is Alicia Fennel's stalker. But we soon discover that he is, in fact, Wallace's biological father and is attempting to get close to his son.

Williams appeared on four episodes during the second season.

The director made a brief cameo as Douglas, the manager of a car rental service who Veronica tries to manipulate for details regarding a case.

Grabeel played Kelly Kuzzio, a closeted 09er who would appear on two episodes throughout the series.

The "Xena: Warrior Princess" star played FBI Agent Morris who takes over the investigation of Duncan Kane's disappearance.

The reality star made her scripted series debut as Kylie Marker, a Neptune High School cheerleader who concocts a blackmail scam in an effort to be out with her girlfriend and also make a few bucks on the side.

Cera played Dean Rudolph, a student at Hearst College who happens to be Veronica and Wallace's tour guide during prospective students day.

But Cera wasn't the only member of the Bluth family to appear on the show...

Shawkat played Stacy Wells, a Hearst student who flirts and hooks up with Veronica's ex-boyfriend Troy (Ashmore). The morning after the hookup, Stacy wakes up to find her hair has been shaved off and that she's been raped. She accuses Troy, who then enlists the help of Veronica to clear his name.

Though Veronica is able to prove Troy's innocence, she's unable to identify the real rapist. This unsolved mystery reopens during the third season of the show.

Strong played Rafe, a Hearst student who participates in a Stanford prison experiment-like study alongside Logan and Wallace.

Lefèvre's character, Marjorie, is a member of the sorority Veronica is investigating as part of the Hearst College rapes.

The actor played Cyrus O'Dell, the dean of Hearst College and an enemy-turned-ally of Veronica.

Begley Jr.'s character appeared on six episodes of the final season.

The former "Are You the One?" host played Mercer Hayes. Viewers are first introduced to Mercer as Logan's charming friend who hosts a radio show and an underground casino. Throughout the series, however, it is revealed that Mercer has drugged and raped a string of female Hearst students. Upon discovering that Veronica knows his identity, Mercer tries to murder her.

Devlin appeared on five episodes of the show.

Hammer's character enlists Veronica's help to find a missing playbook.

Czuchry played Norman Phipps, a reporter who poses as Logan's half-brother in order to get a scoop on a story.

Eggold played Charlie Stone, Logan's actual half-brother.

San Giacomo had a three-episode arc as Harmony Chase, a woman who hires Keith to prove her husband is cheating and falls in love with the PI in the process.

Agron took on the role of Jenny Budosh, a trust fund baby whose plan to cheat Hearst out of thousands in a campus card scam backfires.

Agron appeared on two other episodes during the season.

Shaughnessy played Budd Rose, the husband of a Hearst benefactor who is caught having an affair and blackmailing his wife in the process.

Rudd made a cameo as Desmond Fellows, a former rock star who is trying to make a comeback by touring college campuses.

Ellis portrayed Apollo Bukenya, a Hearst student who quickly rises to fame by writing a book about his time as a child soldier in Uganda. He enlists Veronica's help when a man comes forward claiming to be his father.

The iconic actress had a small role as Gayle Buckley, a lawyer at the firm Veronica is hoping to work for.

O'Connell took on the role of Sheriff Daniel Lamb, the brother of deceased Sheriff Don Lamb. Like Don, Daniel is just as slimy and has just as many issues with the Mars family.

Kristen Bell's husband scored a small cameo in the "Veronica Mars" movie as a guy who tries to hit on Veronica as a club with over the top dance moves.

Starr played Stu "Cobb" Cobbler, a former Neptune High student who was known for dealing drugs. (It's worth noting this character never appeared or was mentioned on the show's three-season run.)