In the films, a great deal of screen time is dedicated to the creation and mass production of these super-soldiers, specifically bred by Saruman for the purpose of murdering absolutely everyone. They're supposedly created by cross-breeding "orcs and goblin-men," though the lack of any scenes portraying orcs and goblin-men fucking is a glaring omission in this process.
We guess that's kind of hot.
Sure enough, the first Uruk-hai off the line gets as badass an introduction as any character in film history. Orcs dig him out of a muddy cocoon, at which point he jumps out and murders the first dude he can find. This soldier has a confirmed kill within five seconds of being born.
He suckled from the teat of murder.
And Saruman creates thousands of them.
After half a film's worth of buildup, we finally see the Uruk-hai in action at the end of Fellowship of the Ring. They pursue the fellowship and manage to kill Boromir.
You know, the guy who got his ass handed to him by two unarmed hobbits.