Zookeeper is a title awarded for completing the Pet Battle meta-achievement World Safari, earned by capturing every battle pet to be found in Kalimdor, the Eastern Kingdoms, Outland, Northrend and Pandaria.
The title appears before your character's name:
World Safari, earned by capturing every battle pet to be found in Kalimdor, the Eastern Kingdoms, Outland, Northrend and Pandaria.
Patch 5.0.4 (2012-08-28): Added. 
