There are three main diverse criminals in the game who have their own personalities, styles, and roles:
Michael De Santa
Michael is a retired bank-robber-turned-father who spends most of his time watching movies in his villa in Los Santos and reminiscing about his glory days of heisting. His marriage is in ruins and he is incapable of connecting with either of his two teenage children. After getting bored with his life of leisure, he return to his old life he's ever really known: crime.
Trevor Phillips
Trevor is a violent drug addict, in his early 40s. He has worked with Michael in the past, and is firmly entrenched in a life of crime. He has experience as a former military pilot and is currently living in Blaine County. He is the 'loose cannon' of the group.
Franklin Clinton
A young rough-and-tumble gangbanger of sorts, Franklin survives by working risky jobs. Franklin wants more from his job.