Captain Ethil Mercaptain is a character in Wasteland 2.
Mercaptain is an expert in weapons, armor and pre-war technology. She has the job of designing new weapons and armor for the Desert Rangers in addition to refurbishing them. She believes Vargas is doing a good job and agrees with his cautious approach.
If you tell her about Ranger Robert Bowling trying to sell guns at a cheap price, she'll have him arrested by two Ranger Gunners. She will also give you any one equipment for just $1 if you have a requisition order.
Her name is a reference to ethyl mercaptan, another name for Ethanethiol.