From WoWWiki

Slither Rock is a small cave found in the far northeastern corner of the Burning Steppes. It is inhabited by a sole creature - the black dragonspawn Cyrus Therepentous. Hidden beyond the Terror Wing Path, Cyrus will nevertheless aid adventurers in vanquishing a common foe, albeit not without an amply supply of rude and derisive comments.

Subzones of Burning Steppes
Altar of Storms • Blackrock Mountain • Blackrock Pass • Blackrock Stronghold • Draco'dar • Dreadmaul Rock • Flame Crest • Morgan's Vigil • The Pillar of Ash • Ruins of Thaurissan • Slither Rock • Terror Wing Path