Who is the main villain of Season 1?

The Master is the main villain of Buffy the Vampire Slayer’s first season. He is an ancient, exceptionally powerful vampire who leads the Order of Aurelius and seeks to open the Hellmouth beneath Sunnydale.

The Master became trapped underground after an earthquake collapsed a church during an earlier attempt to open the Hellmouth. Sunnydale High was later built above the site, making the school a literal center of the supernatural danger surrounding Buffy’s new home. Because he cannot easily leave his lair, he directs followers such as Luke, Darla, and the Anointed One to carry out his plans.

His conflict with Buffy culminates in the season-one finale, “Prophecy Girl.” A prophecy says the Master will kill the Slayer, and he does briefly defeat Buffy by biting her and leaving her in a pool of water. Xander revives her, however, and Buffy returns stronger, defeats the Master, and impales him on a broken table. Adam, Glory, and the Mayor are major villains from later seasons, not season one.