James Nicholas Callis is an English actor. He is known for playing Dr. Gaius Baltar in the re-imagined Battlestar Galactica miniseries and television series, and Bridget Jones's best friend Tom in Bridget Jones's Diary, Bridget Jones: The Edge of Reason, and Bridget Jones's Baby. He joined the cast of the TV series Eureka, on Syfy, in 2010, and since 2017, he has voiced the character Alucard in the Netflix series Castlevania and Castlevania: Nocturne, based on the video game series of the same name. In 2022, he appeared in Season 2 of Star Trek: Picard as Jean-Luc's father in childhood flashbacks.

Dr. Gaius Baltar is a fictional character in the TV series Battlestar Galactica played by James Callis, a reimagining of Lord Baltar from the 1978 Battlestar Galactica series. He is one of the show's primary characters.