Zombie Dog
The Zombie Dog is the first pet the Witch Doctor gets, and is summoned with the Summon Zombie Dog spell.
The WD pet was originally called Mongrel, but was changed during BlizzCon 2009 to Zombie Dog, because it was more descriptive, and actually the original working name within the D3 Team.
The Zombie dog is a good general tank, but is a bit slow on the uptake, and doesn't deal much damage, which can be a problem if you are running through a level. The Witch Doctor can Sacrifice the Zombie Dog to deal damage based on his health.
As many as 4 Mongrels are seen in screen shots and in the gameplay video for a single Witch Woctor, although it is not known what the limits are. In fact, most of the mechanics are not known for sure. Most shots show only 3.
Development
This summon was first seen in the Gameplay Trailer where fans were told that it could be enhanced with the Witch Doctors offensive spells to do additional damage. The Player then demonstrated this by blasting the Mongrel with a Locust Swarm which buffed it, changing its appearance, leaving it covered in a green goo as well as making it cause additional damage with it's regular attack.
Later in the same video the female Witch Doctor is seen hitting her mongrel with a Skull of Flame (although it was called "Fire Bomb" at the time of the trailer) causing it to look fiery and, presumably, do fire damage.
Sometime prior to the Blizzcon 09, this buffing feature was removed. According to Bashiok the feature will not return, and was removed in favor of other buffing methods (runes, passive skills etc.)
