Cthulhu

The image to the right is a concept sketch of  done by Tiy. It was previously thought that the development team intended to add the boss in an update, but it is unknown if this is still planned.

Trivia

 * The concept of Cthulhu was originally devised by author H. P. Lovecraft. The creature is, today, a popular element of Lovecraftian Horror.
 * He is missing one of his eyes. This is because of the Eye of Cthulhu, which was destroyed earlier on.
 * As of the 1.2 update you can fight the Brain of Cthulhu.
 * Cthulhu is probably dead, the Brain of Cthulhu and Eye of Cthulhu is evidence that he probably is, also, The Crimson is rumored to actually be Cthulhu's remains, there is also a skeleton in the background of the Crimson's overworld that closely resembles Cthulhu, further proving this theory.
 * In the most recent spoiler for 1.3, it appears a player is at the dungeon where a token like object depicts a Cthulhu like character on it with four worshippers near it. This could be hinting that Cthulhu might return as part of an event, for more info see Upcoming features
 * According to Lovecraftian canon, Cthulhu is in a state where he is neither dead nor alive, and therefore cannot be killed, it is said that Cthulhu will awaken under certain circumstances, and as such Cthulhu cannot be presumed to never become a boss in the actual game just because it's remains are strewn acros the game.