Cyrus O'Dell was the dean of Hearst College.
Veronica first met Dean O'Dell after she wrote an article for the student paper and the Dean demanded to know her source for the article. After Veronica refused, the Dean threatened to expel her. Veronica eventually made the Dean a deal: Veronica found someone (Weevil) who would repair the Dean's recently vandalized car for free and in exchange Veronica did not have to reveal her source and she was not expelled. The Dean accepted the deal.
The next time Veronica saw the Dean, he needed some help. His stepson needed a bone marrow transplant to live and the only person who could donate on such short notice was Steve, the boy's biological father. Dean O'Dell hired Keith Mars to track Steve down. Upon being found, Steve was unwilling to help his son despite pleas from Dean O'Dell and Mindy, the Dean's wife. Soon after this meeting, Steve went missing and Keith was one of the top suspects in his disappearance. After investigating, Keith discovers that the Dean and his wife knocked Steve out and brought him to the hospital to take the bone marrow forcibly. After Steve gave the bone marrow, the Dean agreed to give him Mindy's car as payment.
The Dean also hired Veronica to discover the location of Selma, the granddaughter of Hearst's founder and one of the members of the Board of Directors, who had gone missing just before a crucial vote about the fate of the Greek system at Hearst. After Selma was found, the vote went through and the Greek system was removed. The Dean was then visited by a wealthy 'benefactor' who pressured Cyrus to reinstate the system. The Dean found a loophole where he was able to cast a final vote and reinstated the Greek system. The Dean was greeted back at school by a bunch of the Lilith House girls who threw spit and eggs at his car.
In Hi, Infidelity, Veronica discovered that Mindy had been having an affair with Hank Landry, Veronica's criminology professor. Veronica kept this information to herself until Spit & Eggs when the Dean hired Keith Mars to find out if Mindy was having an affair. When Keith told Cyrus the news, they drank together until Keith left the Dean to go home. Later that night, the Dean loaded his revolver and went to the hotel room where his wife and Hank Landry were having their affair to confront them. It was not revealed until Papa's Cabin what happened in the hotel room between the Dean, Prof. Landry, and Mindy. The Dean returned to his office and fell asleep on his couch. He was woken up in the middle of the night to the sound of eggs hitting his window. He then saw someone in his office and said, "What are you doing here?" The next morning the Dean was found murdered sitting at his desk by Weevil.
As of Show Me the Monkey, Dean O'Dell's death is believed by the police and his life insurance provider to have been a suicide. A note reading, "Goodbye, cruel world" was left on his computer screen, presumably by the murderer and matching the technique Veronica describes in her "perfect murder" criminology paper. Mindy O'Dell has hired Keith Mars to investigate her husband's death in order to challenge the insurance company's refusal to pay compensation. Keith believes that Dean O'Dell was murdered because the bottle of forty-year-old Scotch whiskey the Dean told him he "lived in anticipation of tasting" was unopened.
In Papa's Cabin, we finally learn that Dean O'Dell had threatened to destroy Landry's career and divorce Mindy leaving her destitute, and Mindy was the mysterious visit in his office, having gone there to beg for clemency, which was when she gave him his Xanax prescription. Despite what appears to be a clear case against Landry and Mindy, it turns out that the Dean was murdered by Hank's TA, Tim Foyle.