Rooftrellen stands for a hero, a role, in the famous Warcraft III customly (fan-made) map DotA (Defense of the Ancients).
He is by some considered to be the most tough hero of the DotA, wearing him "titles" of being indestructible, due to his great quantities of Hit Points, armor, and Hit Point regeneration.
He isn't actually indestructible, but his greatness renders him hard to kill.
- Oftenly being abbreviated as "Roof".
*The game of DotA starts*
Player A: Holy shit! Look at that!
Player B: What?
Player A: That guy just rolled Rooftrellen!
Player B: Ah crap. He's gonna give us hard time!