Ulysses Fonzeheart is the legal custodian of Isabella Karas and a mathematician, physicist and engineer. He lives with Issa in New York.
After the disapperanceof Issa's father, the Professor got custody over Issa. It is implied that at one point he saved her life. How he came to know Issa's father is currently unknown.
He is the voice of reason in Issa's life.