Geary

Geary is a special enemy located near the top of Mount Hellsfont in the Eridium Blight. He takes the form of an unarmed, miniaturized Psycho, has low health and drops 1 of 5 Vault Hunter Heads, these being:
 * Medic Mantis - Commando
 * Alienati0n - Assassin
 * Metal Fear - Siren
 * Marshall Mustache - Gunzerker
 * Fragger - Mechromancer

Golden Gear mini-quest
In either play mode, after starting True Vault Hunter Mode, the fireplace in Claptrap's Place holds a golden gear with the label "Geary's Unbreakable Gear". The item card reads "Only a brisk walk to the Eridium Blight will reward the courier." This is a clue to reach Geary at Mount Hellsfont.

The Golden Gear has hidden rules; once it is picked up, dying or fast travelling will cause the Golden Gear to be lost and fail the "quest". It is allowable to go into Fight For Your Life mode, however. As of Update 1.2.0 (Released 11/13/2012), entering a vehicle fails the "quest".

Once Geary is found, he will attack with (extremely powerful) melee strikes. If the Golden Gear has been picked up and not lost he will only attack once, before rapidly making his way back towards the lava pool with the waterfall and jumping in. After a few seconds, three Rakk will then fly in and each drop a Hyperion loot chest; two are normal, while the middle one always contains purple or E-Tech loot just like the chest in Sanctuary.

Trivia

 * Geary is a reference to Gollum from The Lord of the Rings.

Media
Video: Borderlands 2 How to Get Alienation Head For Zero (tutorial)|Reaching Geary