What is the rank of Commander William Riker?

William Riker holds the rank of Commander during Star Trek: The Next Generation.

Riker is the first officer of the USS Enterprise-D under Captain Jean-Luc Picard. As second-in-command, he oversees many away missions, helps coordinate bridge operations, and is frequently responsible for taking command when Picard is unavailable. His position makes him one of Starfleet's most prominent commanders.

Riker's rank remains Commander throughout the seven-season run of The Next Generation and the associated films set during that era. He is sometimes called “Number One,” a nickname reflecting his role as the captain's first officer rather than a separate rank.

The character later advances to Captain. He accepts command of the USS Titan after Star Trek: Nemesis and is shown commanding other vessels in later Star Trek stories. That later promotion can cause confusion, but for the TNG-era question, Commander is the canonical answer.