William Thomas Riker is a Star Trek: The Next Generation character. He is played by Jonathan Frakes. He is first officer on the starship Enterprise. This means that he is second in command of the starship and can give orders if the Captain is away.
Riker soon becomes very comfortable on the Enterprise, many times refusing offers of his own command. On part 1-2 on the episode "The Best of Both Worlds" Riker takes command on the Enterprise and orders Jean-Luc Picard rescued.