Overseer

The Overseer is a Zerg unit evolved from the Overlord.

The mutation gives it the ability to detect cloaked and burrowed units, along with an increased sight range. However, it loses the Overlord's Creep and Slime abilities.

Game Unit
The Overseer's sight radius expands when it stays stills and shrinks when it moves.

Trivia
The Overseer was developed as the universal Overlord detection in StarCraft I made the Zerg "detectorific". As such, the Overlord/Overseer split makes cloaking more useful to a Zerg's opponent.