He was born to two loving parents, but that didn't last long.
Maniac was not born in a dump. That much is obvious.
At this time, Maniac wasn't known as Maniac. He was Jeffery Lionel Magee. One day, his parents left him with a sitter. Unfortunately, on the way home, they were caught in a trolley accident.
Just like that, Maniac was an orphan. He went to go live with his closest living relatives, Aunt Dot and Uncle Dan. However, they hated each other. They had two of everything because of this, and probably would've had two Jefferies if they could.
Then came the night of the spring musical at Jeffery's school. He started screaming probably from the start, but it wasn't audible until the very end of the chorus.
TALK! TALK! TALK, WILL YA?!
Do, re, me, fa, so, la, ti, doooo ♪
That night, Jeffery ran away. He ran, and he ran. Never again would he return to the house of two toasters.
Or school, for that matter.
Thus, Jeffery ran off to become the legend he is today: "Maniac Magee".