Why Gambit Once Worked for Mr. Sinister in Marvel Comics Lore

Gambit's history with Mr. Sinister starts with a job gone wrong. Before their entanglement deepened, Remy LeBeau worked for Mr. Sinister, also known as Nathaniel Essex, trying to retrieve a diary from a Weapon X facility in Canada. Gambit was appalled by the experiments he saw there, so he burned the diary and told Sinister he had never actually found it.

After being banished, Gambit found his way back to Sinister because his powers were beginning to slip out of his control. That is when Sinister gave Gambit his lobotomy to help him manage those powers.

That act put Gambit in Sinister's debt. Sinister used that leverage to get Gambit to assemble a team called the Marauders, who were sent to massacre the Morlocks under Sinister's command. Gambit tried to stop them, but Sabretooth injured him and left him for dead. He was saved by a young girl who would eventually become the X-Men known as Marrow.