Each character of Buffy the Vampire Slayer corresponds with a character from Hamlet. Here is a guide so you don't get loss while reading:

Hamlet, Prince of Denmark - Buffy Summers, the Vampire Slayer

The Ghost - Joyce Summers

Osric; miscellaneous parts - Dawn Summers

King Claudius - Rupert Giles

Queen Gertrude - Willow Rosenberg

Ophelia - Spike

Polonius - Anya

Laertes - Xander Harris

Horatio - Tara Maclay

Rosencrantz & Guildenstern - Cordelia Chase and Wesley Wyndam-Pryce

Fortinbras - Faith

Gravedigger - Jonathan

Ambassadors to England - Quentin Travers