The Immortal

The Immortal is a character from the Buffyverse, first 'appearing' in the Angel episode "The Girl in Question". The Immortal never appears onscreen throughout the entire episode and is only mentioned. However, from the descriptions we can gather that he is incredibly attractive, athletic, intelligent and also apparently genuinely immortal and unaging. He has accomplished numerous incredible feats and managed to seduce many women, including Darla, Drusilla and Buffy. In Angel Season Five, it is established that Buffy has in fact begun living with the Immortal.

The Immortal also appears in the non-canon novel Queen of the Slayers.

Accomplishments
According to various people that know the Immortal, he has accomplished the following:
 * Spending 150 years in a Tibetan Monastery
 * Climbing Mount Everest several times.
 * Dealing with the Italian Branch of Wolfram and Hart several times and surviving. (The female CEO of the Italian Wolfram and Hart may have been referring to business dealings or a more personal encounter, quite possibly both)
 * "Violating" Drusilla and Darla, not only both of them but both of them at the same time. Something that neither Spike nor Angel could get either girl to agree to.