Zul'rogg

Zul'rogg is a Forest Troll Warlord who was caught in the battle between Sylvanas' forces and those of Varimathras.

A few of his tribesmen were attacked by Sylvanas's force and told her that their chieftain Zul'rogg would avenge them, if they were killed. Sylvanas would later personally encounter Zul'rogg, where he was surrounded by the rest of his forest troll forces.

Current status
While it was possible to take control of him by using a banshee, Sylvanas's hatred of forest trolls could of seen him killed.

As he does not appear in World of Warcraft, Sylvanas may have killed him. Alternatively he could of been enslaved like Mug'thol and Blackthorn and was killed by the Dreadlord Insurgents at some point during the war.

Quotes mentioning Zul'rogg
Sylvanas: "Forest Trolls! I hate them even more than those cursed dreadlords. Slaugther them all!"

Forest Troll: "You'll never get us all, witch! Chieftain Zul'rogg will hunt you down and avenge us!"

Sylvanas: "He's welcome to try, savage!" - Sylavanas: "That brute must be Zul'rogg, the troll chieftain."