Golden gecko (Fallout 2)

"Geckos. The little dudes don't bite hard. It's the Goldens. They go through your leg like an old pipe stem."

- Sulik

The golden gecko is the more beautiful, but also more deadly kind of gecko. As stated by Smiley, the Trapper from the Quest Rescue Smiley the Trapper., they can be found near toxic waste, which they seem to lick up. Though it's not said explicitly, obviously there seems to be a connection between the toxic/radioactive waste and the golden geckos. It can be assumed that exposure to some kind of toxic/radioactive material turns a normal gecko into a golden one.

They can be skinned, if you have the Gecko Skinning perk.