Let me make one thing clear immediately. My novels' protagonist, Thomas O'Shea is a tough guy. I AM NOT. Even though I can bench press 545 pounds, dunk a basketball, and have multiple martial arts awards (not to mention several private black ops successes in dangerous situations), I am not a tough guy. But I do write about tough guys and once taught a course in college called "The Tough Guy Novel."
So, in literature, what makes a tough guy? Basically, he is a man with a code to which he adheres, no matter what. When the code is threatened by criminals, corrupt officials, elements of the underworld, or just evil people, he has three ways to go. He can give in and go along, or he can leave and go someplace new, or he can stand up and fight those who would take him down. We are talking about Robert B. Parker (Spenser), Dashiell Hammett (Sam Spade), Lee Child (Jack Reacher) and William Kent Krueger (Cork O'Connor), among others.
If he gives up, he is lost, and no longer his own man. He could leave, but that would be cowardly. So he stays and digs in and fights.
Many of these tough guys are flawed, and so is mine. Thomas O'Shea has issues with alcohol, women, God, and violence. He is not a private detective, SEAL, cop, or loner. He lost his wife and both daughters to a drunk driver. He was suicidal and angry, but drawn out of his depression when he stumbles onto a farm "accidental" death and starts asking questions. People try to stop him, and thereby a new life for my tough guy is launched.
Someone came up to me once at church, right after the first O'Shea novel (Signs of Struggle) was published, and said, "I'm never gonna mess with you, John. Throwing guys off bridges, shooting people!"
I had to tell him my books are fiction. I even spelled it for him. F-I-C-T-I-O-N. On second thought, I should have just glared and curled a lip and walked away. More fun.