Captain William T. Riker, played by Jonathan Frakes, is a main character on the science-fiction television series Star Trek: The Next Generation. Commander Riker is the first officer of the starship Enterprise, second in command only to Captain Jean-Luc Picard, who affectionately refers to him as "Number One", a term also used by Christopher Pike to refer to his female first officer in the original pilot "The Cage" (played by Majel Barrett). Riker often leads away teams while the captain remains on the ship. In addition to his role in the television series, the character also appears in the Next Generation era Star Trek films, and has made brief appearances on the spin-off series Star Trek: Voyager, and Star Trek: Enterprise.

For the first two seasons, Riker is portrayed as bold and confident, an ambitious young officer in the tradition of James T. Kirk. Over time, Riker's character becomes more reserved, as experience teaches him the wisdom of a patient, careful approach. He becomes comfortable on the Enterprise, repeatedly turning down offers of his own command, and he learns to cherish the company of his fellow officers. Nonetheless, Riker never quite loses his arrogant streak, nor his willingness to occasionally disregard the chain of command.

Riker's background is first explored in the second-season episode, The Icarus Factor. In the episode, Riker's estranged father Kyle visits the Enterprise to offer his son the command of the USS Aries, which Riker refuses. We learn that Riker grew up in Alaska, that his mother Elizabeth died when he was two years old, and that he was raised by his father until the age of 15, when he left home. In the episode, Riker has not spoken with his father for fifteen years, but they manage to partially mend their relationship over a game of martial-arts sparring called Anbo-jyutsu.