The Demoman

Despite being drunk almost all the time and losing his eye to a magic book, Demoman is a monster in the wrong hands,  bringing destruction wherever he goes.

The Demoman is the master of area denial and possibly the most powerful mercenary around. Both his Grenade Launcher and Sticky Launcher do huge amounts of damage. Demomen can work both as offensive and defensive classes, and with their advanced mobility with sticky jumping, their lower speed is negated.

The Demoknight is a sub-class of the Demoman, throwing away his explosive weapons for a sword and shield. But they're not particularly effective.