Answer: Darcy
Mark's surname in Bridget Jones's Diary is Darcy, which is a reference to the character Mr. Darcy from Jane Austen's novel Pride and Prejudice. The character Mark Darcy was created as a modern-day version of Mr. Darcy, with similar personality traits and a love-hate relationship with the main character, Bridget Jones. Interestingly, the actor who played Mark Darcy, Colin Firth, also played Mr. Darcy in the 1995 BBC adaptation of Pride and Prejudice.