William T. Riker (alternates)

Alternate timeline
In an alternate timeline created when the USS Enterprise (NCC-1701-C) was accidentally sent through a temporal rift from 2344 to 2366, the Federation had been at war with the Klingon Empire for almost 20 years as the Enterprise-C's disappearance resulted in the destruction of the Klingon colony Narendra III. In this timeline, Riker was still the first officer of the USS Enterprise (NCC-1701-D). He was killed on the bridge in 2366, while manning a terminal which exploded as a result of heavy Klingon fire. He was helping to buy time for the underpowered Enterprise-C to return through the temporal rift to Narendra III in 2344. 

Alternate realities
In several alternate realities visited by Lieutenant Worf in 2370, Riker was still the Enterprise-D's first officer and threw a surprise birthday party for Worf. In another alternate reality, he was the captain of the Enterprise as Jean-Luc Picard had been killed during the Borg Incursion of 2366-2367.

In another reality, the Borg Collective had succeeded in conquering the Federation and much of the Alpha Quadrant by 2370. The Enterprise, under Riker's command, was one of the last surviving ships. Along with Worf, he was one of its few remaining crewmembers. After it became one of the approximately 285,000 different Enterprises to be sent to the same reality, Riker fired on the Curie as he did not want to return to his own reality. The Enterprise indigenous to that reality then fired on the Borg-infested Enterprise using minimal weapons. This began a chain reaction which resulted in its destruction due to the severe damage which it had suffered in its many engagements with the Borg. 

In another reality in which Riker had failed to stop the Borg, Riker had lost his right eye, many of his crew, and the saucer section of the USS Enterprise-D. Despite his defeat, Riker and the remaining crew continued to help Earth resist the Borg using the Enterprise's battle section. 

In another reality, Riker took command of the FSS in 2365.

In another reality, Riker served aboard the United Earth Space Probe Agency vessel Enterprise before it was captured by the Klingon Empire and became the. His throat was cut by the Klingons. By 2380, Captain Picard was the only surviving member of the original crew.

In another reality, Riker served as the first officer of the USS Enterprise-E, which was under the command of Thomas Halloway, prior to taking command of the USS Titan (alternate reality). As a final parting gift before leaving for the Titan, Riker assigned Lieutenant Commander Picard to bridge duty. This seems to be a similar, if not identical, timeline to the one which Q had shown Picard in 2369, as it is mentioned that Lieutenant Commander Picard had worked extremely hard since Riker and Deanna had evaluated him.

In another reality, Riker was the captain of the USS Enterprise-E in 2380.