From Monkey Island wiki
Reverend Allegro Rasputin is an undead priest at the First Church of LeChuck. While alive, Allegro was a sailor on a ship called the Weeping Iguana. While out on sea, his ship was attacked by LeChuck's ghost ship and Allegro was murdered by LeChuck with his flaming ghost sword and held out his still beating pancreas in front of his face before he died. Although Allegro was at first bitter about becoming a ghost, he later began to admire LeChuck for his powers and skills. He eventually ended up worshiping LeChuck as a god and this inspired him to build the First Church of LeChuck on Monkey Island.
Allegro considers his religion similar to most others, except with more fire, screaming and pointy sticks. He also says that the evil of his religion is the 'Anti-LeChuck' or He-Whose-Name-Must-Not-Be-Spoken (Guybrush Threepwood) who has the number 1138 tattooed on his head. This is a reference to George Lucas's first movie THX 1138 and the Biblical figure of the Anti-Christ, associated with the number 666; plus, Guybrush's title of "He-Whose-Name-Must-Not-Be-Spoken" is a spoof on Lord Voldemort's title of "He-Who-Must-Not-Be-Named" from the Harry Potter series.
Allegro is the Italian for cheerful; it is also used in music to refer to a quick and lively tempo. In history, (Grigori) Rasputin was a Russian monk who was renowned for his mystic and occult practices.