Background
Montgomery (aka "Mom") Tanks comes from a small farm on the Outer Rim. His father was a Mandalorian in the classic sense. A ruthless bounty hunter who thrived on superior force of arms, until one day he didn't.
Left broken and alone in a hospital, he was tended to everyday by a concerned doctor. Eventually a bond was formed between them. When he recovered, he used his blood money to buy a small farm and settle down and start a new life.
As kids, Mom was often the one chasing after the younger brothers, keeping them out of harm's way (especially Dom). More often than not, this meant he found himself in more fistfights and scrapes than he cared to admit. As a result, he focused his combat training on CQC rather than marksmanship.
After the destruction of Alderaan, Mom tore through the galaxy, bringing justice to those who were wronged by the same people who would openly destroy an entire planet. The wanton murder of Imperial soldiers saw Mom arrested and sentenced to death.
Motivation
Beliefs — Justice
"The character has a strong, unshakable sense of right and wrong, and he sees the injustices of Imperial rule throughout the galaxy. He is committed to seeing justice brought back to the galaxy, and he wishes those who have betrayed it to receive the punishment they deserve." (AoR, 105)
Since the destruction of Alderaan, Mom saw the Empire for what it was—a bully. He ensured that he would do everything in his power to see the end to their reign of terror.
Duties
Personnel - 0
"More than machines, credits, or information, the people of the Alliance are the most important and vital assets there are, and the Player Character knows this. He is devoted to seeing to their safety, well-being, and capacity for success. No one should ever be left behind: the most successful missions might not achieve every goal, but they are successful nonetheless when no one dies." (AoR, 47)
Mom's instinct to protect those against bullies spreads to protecting the people he fight alongside with.
Description