Officer Shallowgrave is a former truancy officer with a grudge against Catman and Timmy for making him lose his job.
Shallowgrave was first seen stalking Timmy and Catman(who was a kid at that point) when they were seen skipping school. When Timmy unwished his wish and proved that he was with an adult the entire time, Shallowgrave swore revenge before taking off. Due to the fact that he was stalking a child who was technically with an adult, Shallowgrave was fired from his job as a truant officer. Afterward, he got a new job at the F.U.N. (For Unruly Ne'er-Do-Wells) Academy. He is a scary looking cop who wanted to return Timmy and Catman to school at first, but is currently a drill instructor at F.U.N. Academy where he made Timmy and his friends go through a lot of drill exercises.
Shallowgrave has a patch over his robotic eye, which has a long scar running through it up and down his face. He is also missing some teeth. He is husky, has gray hair, and wears black detectives clothing and hat with a gold truancy officer's badge. His left hand is a hook, and he has a number of weapon replacements for his hook inside his jacket.
One time Timmy Turner had wished Catman down to a kid's size so that they could go on an adventure together, during a school day no less. Principal Waxelplax saw Timmy Turner and the mysterious Catkid playing hooky, and sent Shallowgrave after them. While having fun around town, Timmy and Catkid ran into Shallowgrave on numerous occasions, but managed to elude him every time. Eventually after Catman was returned to normal size, he threatened Shallowgrave to back off and "pick on someone (his) own size". After an angry stare and growl from Shallowgrave, Catman nervously said "besides me", and then Shallowgrave's hook turned into a rocket and he flew off.
Shallowgrave appeared again working as a drill instructor at Remy Buxaplenty's F.U.N. Academy. He is the instructor there and not a truant officer anymore because Timmy was the reason he lost his previous job. He made the trials that Timmy and his friends had to go through hard due to Remy bribing him and even threatened to blow up the shack that Cosmo and Wanda were trapped in should they fail to complete one trial in a time limit. Timmy and his friends manage to win and save Cosmo and Wanda from being killed which results the missiles hitting Remy, his fairy godparent Juandissimo, Shallowgrave and later Mr. Crocker . Timmy then wished to unwish the wish about him and his friend going to F.U.N. Academy, allowing Timmy and his friends to become free again.
In "Go Young, West Man" it is shown the Shallowgrave has different types of hooks to bring students dead, but he doesn't have any for alive and because of that he charged Waxelplax extra to get a hook for bringing students alive.
He apparently has had quite a couple times with Timmy, as he appears to have hated him straight from his debut. Though somehow Cosmo doesn't seem to know him.