updated: 05/02/2007
Drusilla (Juliet Landau) first turned up in Sunnydale with Spike during the second season of Buffy. But it soon became clear than both of them had a backstory with both Angel and Darla. It was later revealed that Darla was the vampire who made Angel who in turn made Drusilla; so when Drusilla remade Darla in ‘The Trial’, Darla became both her vampiric grandmother and her daughter: no wonder they’re a strange pair.
Like Darla, Drusilla survived her encounters with the Slayer to become of the very few recurring vampire characters in Buffy, and then made the transition to being a recurring character in Angel.