Thomas Riker is the duplicate of Will Riker, a starfleet commander that serves as Captain Picard's Number One officer aboard the USS Enterprise. He appeared in Star Trek: The Next Generation.
Thomas Riker's life and experiences were the same as William T. Riker's prior to 2361. In that year, William Riker, at the time a lieutenant assigned to the USS Potemkin, was leading an evacuation mission on the planet Nervala IV. The planet was notorious for its atmospheric distortion field which prevented the use of transporters and shuttles except for brief periods every eight years. During Riker's transport from the planet's surface, a second confinement beam was initiated to overcome these difficulties, with the intent of reintegrating the two beams in the transporter buffer prior to rematerialization on the ship. However, the modulation of the distortion field caused only one transporter signal to correctly materialize on the Potemkin – the second signal bounced off of the field and rematerialized on the planet's surface, unbeknownst to the rest of the crew. As a result, two identical William Thomas Rikers were created; one materialized aboard the Potemkin, and the other was left on the planet's surface, his existence going unnoticed by the crew of the Potemkin. Because the split between signals resulted in an equal distribution of Riker's transporter pattern, both of them had an equally legitimate claim to being the "real" William T. Riker.
The existence of this other William Riker (hereafter referred to as "Thomas") was discovered on Nervala IV eight years later in 2369 when the USS Enterprise-D returned to retrieve scientific research that had been left behind. With the aid of Thomas, who had altered the computer systems on the planet to aid in his survival, the Enterprise away team was able to access the information and return to the ship with Thomas.
Relationship with Deanna Troi
During the time he spent on the planet, Thomas had remained deeply in love with Deanna Troi, his girlfriend at the time. Thomas had planned to meet Deanna on Risa the year of the transporter mishap, a fact upon which he had dwelt while stranded. In contrast, the Riker that beamed off-planet eight years prior was soon promoted and made his career a priority over their relationship, and never made the trip to Risa with Deanna.
Upon his rescue, Thomas told Deanna that he could not believe he had failed to meet her as planned and that he was hoping their relationship could resume. Initially, Deanna was opposed to the idea, but found herself won over despite her objections. In the end, however, Thomas decided that he could not remain on the Enterprise, while Troi's feelings for him were not strong enough for her to leave the Enterprise with him.
Thomas and William clashed almost immediately due to the resentment each felt towards the other. The eight years of living different lives made them entirely different men – William evolved into a cautious and duty-driven officer while Thomas remained impulsive and reckless. As a result of conflicts with William – who was by that time a superior officer (a Commander) – Lieutenant Riker decided to leave the Enterprise. He chose to use his middle name, Thomas, to distinguish himself from his transporter duplicate. Captain Jean-Luc Picard managed to get Thomas a posting on the USS Gandhi where he could continue his Starfleet career. Upon Thomas' departure, William seemed to have accepted Thomas' existence and gave him his trombone as a parting gift.
In 2370, Thomas expressed dismay at the Federation's policies towards the Cardassians and the Federation colonies in the Demilitarized Zone, and later joined the Maquis resistance. In early 2371, Thomas, posing as William Riker, came aboard Deep Space 9 and stole the newly commissioned USS Defiant.
With Major Kira as his unwilling passenger, Thomas took the Defiant to the Orias system, deep in Cardassian space, where the Maquis believed that the Cardassians were building a fleet of warships. Trying to locate the Defiant with the assistance of Commander Sisko, Gul Dukat swore that he knew nothing of this fleet. He was telling the truth, as the fleet had been constructed by the Obsidian Order in direct violation of Cardassian law. As the Defiant arrived at Orias, it was intercepted by a number of Cardassian warships.
Sisko achieved a compromise with Dukat and negotiated Thomas' surrender – in exchange for the Defiant's sensor scans of the secretive Orias base, Thomas' sentence would be reduced to life imprisonment in a labor camp on Lazon II, while the Defiant would be escorted back to the Federation-Cardassian border returning the rest of the Maquis crew to the Federation for trial.
Immediately after Thomas surrendered the Defiant to the Galor-class cruisers of the Cardassian Central Command, the Kraxon extended its shields around the Defiant to protect her from the fast approaching ships from Orias (upgraded Keldon class cruisers with markedly higher top speeds than regular ships of its class). Upon seeing this, the ships from Orias – under the command of the Obsidian Order and not technically part of the Cardassian military – turned around and returned to the Orias system.
Just before Thomas transported over to the Kraxon, Kira promised to return for him one day, but it is not known whether she ever did.