William Thomas Riker is a character in the fictional Star Trek universe played by Jonathan Frakes, who appears in the television series Star Trek: The Next Generation (TNG) and all the movies focussing on the TNG characters. He is the First Officer, under Captain Jean-Luc Picard, of two incarnations of the starship Enterprise - the USS Enterprise (NCC 1701-D) and the USS Enterprise (NCC 1701-E).

In the movie Star Trek: Nemesis, having previously turned down several promotions in order to continue serving with Picard, he becomes captain of the USS Titan.