When we first meet Maman, there's a chance he might not be such a bad dude. He smiles a lot, has cool sunglasses, and offers Jamal, Salim, and Latika cold sodas, warm meals, and a place to sleep that isn't a literal dump.
But appearances can be deceiving. As it happens, Maman runs a ring of child beggars, in which he enlists our protagonists. If that doesn't make him unlikeable enough, he even gruesomely blinds certain children in order to maximize profits.
Maman sees potential in Salim, recruiting him as a sort of trustee to help keep the other children in line. But Salim turns on him when he realizes that Maman has plans to blind his little bro. Salim is able to escape with Jamal, but Latika is left behind.
We revisit Maman some years later, when Jamal enlists Salim to help find Latika. It turns out that Latika is now Maman's "prized possession," being groomed to become a high-class prostitute. Jamal and Salim are able to locate and rescue Latika, after Salim gets the drop on Maman, killing his old mentor with a cold-blooded shot to the head:
SALIM: Maman never forgets, isn't that right?
MAMAN: Maman can make an exception.
SALIM: I can't take that risk.
There's no doubt that Maman is cruel, barbaric, and otherwise completely despicable. Yet it is his death that marks Salim's point of no return. Maman was training Salim to be a killer—and unfortunately for the gangster, he was successful.