James is seeming of average height and is Caucasian. He has brown eyes, graying brown hair and appears to be in his 40s.
James was a friendly, easygoing, and occasionally absentminded man. He was always very encouraging of his children's hobbies and desire to learn, because as he was often known to say, "Anything is possible for a Possible."
Like any father, he is protective of his daughter and doesn't like it when she spends time with boys. Unfortunately, this also extends to James treating his "Kimmie-cub" like she's still a little girl and all but refusing to accept she's growing up. He eventually comes to accept that Kim isn't a child anymore but he still calls her "kimmie-cub" and is there for her.
James believes strongly in family bonds and expects the same of his children, such as honoring family commitments.
A brilliant scientist, if a bit inattentive at times, James was part of a team of researchers at the Middleton Space Center. When a problem fell within his area of expertise, he was always a valuable asset to Kim in her fight against evil.
James had a habit of leaning on equipment and accidentally activating it. He has launched a rocket a week ahead of schedule, caused a super magnet to de-pants Ron, and almost deleted the Hephaestus Program, which he had been working on for a number of years, from his computer.
James graduated from the Middleton Institute of Science and Technologies. In college, he knew a young Drew Lipsky, who would eventually become the supervillain, Dr. Drakken. It was the scornful laughter of James and his friends, Bob Chen and Ramesh that supposedly drove Drew over the edge after he had embarrassed himself through his invention of 'robot dates' who would later become the Bebe robots.
He has a wife, Ann, a daughter, Kim, whom he calls his "Kimmie-cub", and his twin sons, Jim and Tim, named after him. His mother, Nana Possible, lives in Florida. His older brother, Slim Possible, lives on a ranch in Montana, along with his niece Joss. It is unclear whether Larry and his mother Aunt June are related to James or his wife.
Though Kim loved her father, she was sometimes embarrassed by his affection and desire to be close to her. She was also greatly frustrated by his tendency to see her as his little girl, even after she was well into high school. Dr. Possible was very protective of Kim when it came to her dating, despite being very uncomfortable discussing boys with Kim himself.
Jim and Tim seemed to take more after their father, as they spent much time building experimental rockets around the house, occasionally borrowing some of Dr. Possible's tools from work to do so.
He has an overall friendly relationship with his colleagues from the Middleton Space Center, and his old college pals Chen and Ramesh.
Though sometimes visibly annoyed with how often Ron would pop in uninvited to meals, James did not really seem to mind his presence around the Possible home. Still, he felt the need to at least threaten Ron after he began dating Kim.
Dr. Drakken still considered James an enemy, and James is all-too-happy to call Drakken "Drew" to his face, just to spite him.
His married life was stable and loving, with no signs of conflict between himself and his wife.