Alice is a hybrid of all supernatural creatures. She's been alive since before the Mikaelsons ever existed. She was turned into a vampire the same way the Mikaelsons were. Back when she was only part witch and part werewolf her 'brother' stabbed her with a knife laced with the immortality potion on it. When she heard of a witch trying to turn her kids into vampires she went and asked her to turn her first. She than became part Witch, part Werewolf, and part vampire. After word got around about her people started calling her the Ultimate Hybrid.