Eli is the narrator of The Sisters Brothers, and, as befits this role, he is observant, sensitive, and perceptive and he has a lot to say. At the beginning of the book, he talks about the death of his horse, showing his sympathy for the animal and the anguish he felt at its painful end:
I was very fond of my previous horse and lately had been experiencing visions while I slept of his death, his kicking, burning legs, his hot, popping eyeballs.
This sensitivity and attachment to his horse does not bode well for Eli's career as a hired assassin. The environment depicted in the novel, that of California during the Gold Rush in the 1850s, is a tough one, and Eli is not over-scrupulous. He does what it takes to survive. Nonetheless, he does not enjoy being a hired gun and is relieved when, later in the book, he is able to escape from this grim trade.
Charlie is a tougher, more brutal character than his brother. He is forbidding in manner and laconic in speech, the stereotype of rugged masculinity. When he tells Eli about the conditions of the job they are to do, he bluntly states:
"I'm to be lead man on this one, Eli."
"Who says so?"
"Commodore says so."
I drank my brandy. "What's it mean?"
"It means I am in charge."
"What's it mean about money?"
"More for me."
Eli says that Charlie "can be uncommonly cruel with his tongue," though he prefers to express himself through physical violence. He has no conscience or sensitivity, is prepared to do anything to survive, and defines himself through his strength and masculinity.