Luke, The Vessel:

Debut -- Welcome to the Hellmouth (Season 1)

Death -- The Harvest (Season 1)

Luke was one of the first vampires that Buffy faced upon moving to Sunnydale. He summoned The Master up from a pool of water deep within the bowels of the earth. Because he was then the strongest of The Master's brood, he was chosen to become "The Vessel" -- each life he took would imbue The Master with enough power to break free of and open the Hellmouth. Buffy first meets Luke in the mausoleum and manages to escape from him. The next night, Luke leads the other vampires to the Bronze to accomplish said task of empowering The Master. It is here that Buffy triumphs over Luke.

Most Ironic Quote:

"I'll handle the little girl."

Interestingly enough, the actor who portrayed Luke, Brian Thompson, appears again in Season 2, in another 2-part episode -- Surprise and Innocence playing another evildoer known as The Judge.