Special Agent Tim "Sully" Sullivan is an FBI agent introduced in the second season to be Dr. Brennan's love interest. He makes four consecutive appearances in the second season starting with episode "The Girl in the Gator", where he works with Dr. Brennan in a case while Booth is in therapy. Brennan doubted his sincerity at first because of his wide variety of interests and hobbies, but Booth assured her that Sully is serious about his job. He tells her that Sully lost his partner the year before and that causes him to look for a life beyond the FBI.
After closing the case, Sully asks Brennan out on a date, which she eagerly agrees to. Their relationship becomes more serious and in episode "The Boneless Bride in the River", Sully asks Brennan to go with him to the Caribbean in his new boat which he named after her, but she refuses. He tells Brennan that he will come back in a year's time but he never returned until ten years after.
He is mentioned in "The Glowing Bones in the Old Stone House" as Brennan says she and Sully have been to a trendy restaurant, whose famous chef has been murdered. Angela later asks her best friend if she regrets letting him go, a question that Brennan evades.
Sully returns in The Grief and the Girl, having heard about Brennan's father's death. He flew in to check up on her. It was revealed that he has resigned from the FBI and now owns a sandwich shop and is in a relationship with a 28-year old oboe player. He eventually left and promised Brennan to keep in touch.
- Sully named a sandwich after Booth; a triple decker with roast beef on rye with pastrami and Swiss cheese. He also named one after Brennan called the "Tempe Tempeh."
- Aubrey admired Sully as a new idol for being a professional sandwich maker.
- Sully was the first recurring character who lasted the longest time unaccounted for for ten years before returning.
- The character was likely named after the famous American Civil War photographer; Timothy O' Sullivan.