Captain Mitchell is the second son of his family. He married Reina Mitchell and have their first child, Ryan. When Reina died, he married Jasmine, Reina's twin sister (which he did not know at the time) and had their first child, Brian. In the government want William to built an underwater base in Mariner Bay in the year 1996.
Captain Mitchell is Causisan, with short black hair. He wore a navy uniform.
- Mitchell is the first known Power Rangers Mentor to be a parent of a Ranger. Later, Sensei Kanoi Watanabe, father of Cameron Watanabe in Ninja Storm and Andrew Hartford, father of Mack Hartford in Operation Overdrive follow in his footsteps.
- It should also be noted that Captain Mitchell is the first human mentor of the Power Rangers franchise.
- Ron Roggé, his actor, did not reprise his role during the Lightspeed Rescue and Time Force teamup, but instead played the voice of Quargonon in the episode instead.
- It is implied in A Matter of Trust that Captain Mitchell is a former widower, his wife having died sometime when Ryan, Jane and Dana were very young.