Dr. Terrible

Dr. Terrible was a mad scientist in the Underhalls in Icecrown, more specific in the Hall of Horrors. He was the author of [Dr. Terrible's "Building a Better Flesh Giant"], and carried out experiments on vargul parts in order to build a powerful Flesh Giants. He created the Flesh Giant Nergeld and wantsed to create an army of these things. However, the adventurer intervened and killed him by using his own creation against him.^[2]

Objective of

Apprentice Osterkilgr drops [Dr. Terrible's "Building a Better Flesh Giant"], that starts this quest. You then ride the prototype flesh giant until Dr. Terrible comes along to try and stop you.

Dr. Terrible needs to be killed for the quest [25-30] The Sum is Greater than the Parts.

Crazed Chop — Delivers a crazed overhead chop, causing 150% weapon damage to an enemy and knocking them down.
Heal — Calls upon Holy magic to heal an ally.
Slime Stream — Deals 5 Nature damage every 3 sec for 18 sec.

On spawn: WHO DARES?! I AM GOING TO FLAY THE FLESH FROM YOUR BONES EVEN IF I HAVE TO DESTROY NERGELD TO GET TO YOU!

On death:

I'LL RISE AGAIN AND WHEN I DO I WILL HAVE MY REVENGE!

The name "Dr. Terrible" appears in at least one TV show (from 2001). However, the Dr. Horrible's Sing-Along Blog musical web miniseries was being produced and published in mid 2008, shortly before the WotLK expansion was released. It is possible that this name was inspired by the series.
He appears to do an evil laugh upon killing a player.
Note that if another player aggros him and is killed while you ride Nergeld, it will annoyingly cause Nergeld to die and reset the encounter.