Born in 2222, Forty is Eulogy's second in command and earned his nickname from the fact that, throughout his life, he has killed 40 men. However, killing slaves is something Forty considers "sport" and doesn't count toward his total.
If you have the Paradise Falls box key in your possession and fail an attempt to pickpocket Forty, he will approach you and take the key away. You will then be informed that it has been removed from your inventory.
Forty has noticeably more health than the average human opponent, although not to an exceptional degree.
Every now and then, you can see Eulogy walk out of his pad, and he will say he's going to talk to Forty. If you follow Eulogy outside, you will see Eulogy and Forty argue.