"Now join your brother...INSIDE THE PAINTING!"
--King Boo in Luigi's mansion
King Boo 1
King Boo was born Prince Pear, son of King Apple, the king of the Mushroom Kingdom. When King Apple died Prince Pear became king.
King Pear was a kind king and everyone in the mushroom kingdom was happy. Pear had a daughter he named Peach. Princess Peach. However it was later discovered that Peach had a horrible disease making her a hybrid spider-rat creature. She soon had a spell cast on herself though making her look human. Later Peach killed her father so she became Queen Peach.
Pear became a ghost, then became their king. He is working to destroy Peach. But he was a twisted soul, and not only worked to destroy Peach, but destroyed anybody his path. Over the years, the lighthearted soul became a twisted, dark and evil ghost.
King Boo 2
King Boo 2 was born a poor person in the Mushroom Kingdom.
He became a merchant living in Isle Delfino. He was later killed by Princess Peach for questioning her.
King Boo 1 was gone so the boo's needed a new king. The man, now a ghost became king and made a debut in Super Mario Sunshine. Later on, King Boo 1 escaped from his painting, deafeated King Boo 2.
King Boo 1's Return
King Boo 1 escaped from his painting and took the role of King Boo again.