Though not as heavily featured as the rest of the main cast, Sheldon Oswald Lee (voiced by Quinton Flynn) arguably qualifies as a core member of the group. Sheldon is Jenny's self-proclaimed romantic admirer. However, no matter what he tries, Jenny still refuses his romantic advances, though she does care for him as a friend.
Being skilled in robotics, Sheldon has created gadgets and modifications for Jenny, usually very unnecessarily bulky and extravagant, as well as doing minor repair work. He has even done more extreme modifications when requested by XJ-9, usually when Dr. Wakeman refuses to do them herself.
His skill has led to his creating a robotic alter-ego, The Silver Shell. Sheldon originally created the identity in an attempt to convince Jenny that robot boys were jerks, though this backfired when Jenny's affection for the robot grew even greater. As a hero, the Silver Shell has an imposing appearance, and a 'smooth' demeanor, and an excess of confidence, all qualities the human Sheldon lacks in his normal guise.
Although his age in the series is confirmed to be 15, a mishap in the space-time continuum caused him to live 75 years in space, doing odd jobs to earn money, and even captaining a space pirate ship. Due to the theory of relativity, he returns to Earth as an old man, while Jenny and the others haven't aged a day. Using Wakeman's age reverser, Jenny accidentally de-ages him into an infant. His space pirate crew returns and takes him into space to age him further. One day later he is 15 again. Therefore, his true age is about 105.
In an interview with Rob Renzetti, he revealed that he and his team would've loved to see Sheldon and Jenny as a couple before the series' premature cancellation.
Crush On Jenny
Sheldon has crush on Jenny ever since he met her, because she saved him from a bunch of bullies ( Attack of the 5 1/2 foot geek ). He was the only one at Tremorton High besides Brad that wasn't afraid/hated her from day one. He always tries to impress her with the latest gadgets and designs for improving Jenny's crime fighting abilities but always ends up ruining everything. In one episode it is seen very clearly that Jenny finds out about Sheldon's true feelings toward her and decides to take up his offer, but unable to hear what he says results in her incorrectly hearing him and thinks that he is refusing to go out with her and then storms off mad, leaving Sheldon confused and thinking that he has just messed up having a relationship with her.
Sheldon has always been a geek and a easy target to being bullied. In fact if it wasnt for him being a nerd he would have never meet Jenny. The episode that they first meet in shows him being bullied and them throwing his toy robot around. Jenny then comes up and asks why they are bullying Sheldon and when they ignore her question she catches the toy robot and tells them to go away. Sheldon was shocked and impressed by Jennys abilitys He fixes her problem (she had a screw loose) and develops a crush on her and from then on tries to impress her with his geeky way.
MLAATR Christmas Special
Sheldon was part of the group responsible for capturing Jenny after a little boy took her home the previous Christmas. Jenny had destroyed every holiday prior except fathers day.