William Riker is a 2nd generation Replicant, created by Bob after the battle in Epsilon Eridani against Medieros. Riker is the first to volunteer to go back to earth and check on the other humans, and leads the mission to evacuate earth after.
Riker named himself based off Star Trek character William T. Riker. Riker buys in heavily to the Star Trek theme, using a Star Trek command center as his VR and wearing a Star Trek Captain uniform.
Riker is one of the more serious of the Bob replicants, butting heads early with Milo and his own replicant, Homer. Riker volunteers to go back to earth and find out what happened to the human race, treating the survival of his home as a mission he is tasked to complete.