tarrasque

One of the most infamous and powerful monsters from the Dungeons & Dragons roleplaying game. Like other monsters, specifics of its appearance and power vary between versions, but it usually appears as a unique, gigantic bipedal reptilian creature. It is also immensely strong and tough even for its size, and in some versions, the means to truly kill it are unknown.

A popular monster girl version of the Tarrasque appared in the story "Taming a Tarrasque" by ELH, which he wrote for the Monster Girl General community. That story can be read on AO3 or Pastebin:

https://archiveofourown.org/works/94088411
https://pastebin.com/KMYvY8Ds

It proved popular enough to inspire several works of art, mostly by less. His version remains the most popular depiction.