Star Trek: The Next Generation wanted William T. Riker had to appeal to fans of The Original Series
When Star Trek: The Next Generation was in production, the producers knew they would need to draw in fans of The Original Series. Those fans had gotten used to a self-assured, handsome man with an almost magnetic attraction for ladies because of Captain James T. Kirk. So when Jonathan Frakes came onboard for the role of Commander William T. Riker, they gave him the same confidence and attitude, but the producers wanted to take things just a little further so that, hopefully, fans would make a connection. According to Whatculture, that’s why they gave Riker the same middle initial as Captain Kirk.
While it might seem silly now, back in 1986 and 1987 before the series debuted, there was a lot of uncertainty as to whether or not it would draw in a following. Many fans had already vehemently declared they would not watch the new series without the original cast. So producers thought drawing parallels between the two series would help, and this was just one of the ways they came up with.
The “T” in William T. Riker didn’t have a name until the sixth season of The Next Generation
Over the years, the production staff bandied names about that they thought would fit for the commander’s middle name. They came up with Thelonius, based on the jazz musician Thelonius Monk as a nod to Riker’s love of jazz. (Even though he didn’t have a love of jazz when he was an infant which is when he would have been given the middle name). And even considered Tecumseh. Possibly they meant for Number One to have a Native American connection, but that never came to pass.
Finally, in the sixth season of the series, the staff settled on Thomas. Maybe because it was easiest, or they just got tired of trying to come up with a unique one that would fit only the commander. At any rate, he might not have had the creative middle name like James Tiberius Kirk did, but Riker did have a lot of the swagger and self-assuredness that Kirk had possessed. And that gave him all the connection he needed.