Master (Buffy)
One of the oldest vampires on record, the Master led the Order of Aurelius, and lurked below paying tribute to the Old Ones. His name in life was Heinrich Joseph Nest. He sired many vampires including Darla, who sired Angelus, who in turn sired Drusilla, whom sired Spike.
In 1937, the Master journeyed to a church in Sunnydale and attempted to open the Hellmouth, which would bring the Old Ones back to Earth. He was stopped by an earthquake, which buried the church along with the Master deep beneath Sunnydale. The Master himself became trapped between Earth and Hell like a cork in a bottle. In 1997, the Master awoke after a long slumber at the time of the Harvest and sent a group of vampires, led by Luke, to feed off the partygoers at the Bronze to give him the strength to free himself. They were defeated by a young Slayer named Buffy Summers. The Master enacted many schemes to free himself and rid himself of the Slayer, including sending the Three after her and sending Darla to deal with them personally.
Around the time of Sunnydale High's Spring Fling, Buffy learned of a prophecy that the Master would rise and she would die. While hesitant to fight him, she voluntarily allowed the Anointed One to lead her to the Master in the hopes of slaying him and preventing his ascension. The Master easily overpowered Buffy and fed off of her before killing her. Her blood was what freed him and began to open the Hellmouth. Buffy was revived by Xander Harris, who administered CPR to her. She made her way to the roof of Sunnydale High to confront and finally slay the Master, thus closing the Hellmouth.
His bones were buried on consecrated ground, but were stolen by vampires that served the Anointed One in an attempt to resurrect him. Buffy defeated the vampires and shattered the Master's bones. The Master is seemingly permanently gone.
Alternate Timelines
In an alternate universe created by Cordelia Chase's wish (granted by Anya) that Buffy never came to Sunnydale, the Master was freed, and ruled Sunnydale by night while keeping the populace in fear by day. Vampiric versions of Willow Rosenberg and Xander were among his favorites. Buffy was called in to defeat him several years too late, and she was killed by the Master, just before Rupert Giles could undo Cordelia's wish and restore reality to normal.
