Anytime a science fiction series brings up the name “Pegasus”, you’re in for a bad time. Riker is one of the few survivors of the Pegasus Incident. The Pegasus was conducting illegal experiments, and a majority of the crew mutinied to stop then-Captain Erik Pressman. Most of the crew died following that, with the ship getting stuck in an astroid after an issue with an illegal cloaking device. Riker, being just an ensign at the time survived, but after some time on the Enterprise, was later forced to confront Pressman for his activities. It resulted in one of the better episodes of the series, as Riker had to come face to face with the realities of his time on the Pegasus.
In a prelude to Season 3’s Best of Both Worlds finale, the crew of the Enterprise decide to conduct a war games scenario, with Picard taking the Enterprise and Riker taking the Hathaway. It’s a wonderful episode that shows off just how good Riker could be in charge, even though he regularly refuses any such promotion.