Decker was portrayed in the film by Stephen Collins.
Will Decker was the son of Starfleet Commodore Matthew Decker and Joan Decker. Decker's father was away for most of his childhood serving in Starfleet, and his mother was the one who raised him. Decker decided to follow in his father's footsteps, and entered Starfleet. In the 2250s Decker served as a cadet on the starship USS Discovery.
His father died in 2267 fighting against a Planet Killer that was destroying planets in Federation space.
He was considered a man of very high ideals, who wanted to explore the potential of the human mind and how diversity could advance not only the human species, but other species as well.
As a Lieutenant Commander, Decker participated in a Starfleet mission to Delta IV, where he became involved with a young Deltan woman named Ilia. Decker ended the relationship, leaving Ilia without saying goodbye. Decker became friends with Captain James T. Kirk during this time.
When the Enterprise returned to Earth in 2270 Starfleet decided instead of dismantling the Enterprise to instead perform a major refit of its most famous starship. By then a Captain, Decker was assigned command of the Enterprise for its 18 month refit. With the help of Nyota Uhura, Decker recruited the most diverse crew in Starfleet to that point to staff the refitted Enterprise.
As Starfleet completed the refit of the Enterprise the alien menace V'Ger approached Earth. Kirk persuaded Starfleet to give him back the Enterprise. Kirk had Decker stay on board as his executive officer. Decker resented how Kirk had taken back command from Kirk. Additionally Ilia came on board as their new navigator, adding to the discomfort Decker felt. Decker resolved to remain professional about the entire situation, and do his duty to the best of his ability.
After Ilia was taken off the Enterprise by V'Ger and replaced by a probe that had her memories and experiences, Decker worked with Ilia to try to draw out her personality from beneath that of the probe's.
V'Ger as revealed to be the long lost probe Voyager VI. When the probe decided that either its creator merge with it or it would destroy Earth, Decker decided to offer himself for merging in order to save humanity. Telling Kirk that he wanted the merging as much as Kirk wanted the Enterprise, Decker allowed V'Ger to absorb him and Ilia to create a new life form named Voyager. Voyager departed from the physical plane of existence. Kirk subsequently listed Decker and Ilia as missing in his report to Starfleet.
Kirk felt awkward about having to call Joan Decker, not feeling fully able to express what had happened. He was the one who had notified her of her husband's death, and now he had to tell her that Decker wouldn't be coming home. A few weeks later, when working to defuse a hostage situation on the Fabrini generational ship Yonada, Spock came in to contact with the merged Voyager. He later told Kirk that Decker was happy in his new existence. Kirk would later talk further with Decker's mother, and learned much more about Decker.
- Willard Decker was originally going to be the first officer in the Star Trek Phase II television series. Later when Star Trek: The Next Generation was developed parts of the backstory for Decker were adapted for the role of William Riker. During the first season writers duplicated many of Decker's character traits for Riker.