Buffyverse by HoH

Question 12

A young Rupert Giles had the mark of THIS DEMON tattooed on himself, and along with Ethan Rayne and others, summoned him in order to get high. He came to Sunnydale in the season two episode The Dark Age to kill Giles and Ethan, but was ultimately thwarted. He escaped, however, and grew more powerful, becoming a Big Bad in Angel & Faith, where he was finally killed by Angel, we think. Who is this?