In ancient myths, the Chimera was killed by Bellerphon on Pegasus when Bellerophon jammed a lead ball into its mouth. The ball melted, killing it with lead poison and suffocation. The original Chimera died long ago at the hands of the hero Bellerophon, though lesser Chimera still prowl the labyrinth of Crete.
Percy is cornered by a fat lady and her pet Chihuahua at the top of the Gateway Arch. The lady constantly refers to her pet as "sonny" or "son" and it is only when Percy is forced to wait for a second elevator down, and left without the company of Grover Underwood and Annabeth Chase that he discovers that the fat lady really is Echidna, mother of all monsters.
The Chihuahua transforms into his true form, that of the Chimera, and attacks Percy. As Percy tries to defend himself and a few innocent bystanders with Riptide, he is outwitted by the creature and ultimately forced to dive out of the Gateway Arch (via a hole conveniently provided by the Chimera) into the Mississippi after being poisoned by the snake-headed tail.
The Chimera has the head of a lion, the body of a goat, a blood-caked mane, and a ten-foot-long diamondback snake-headed tail which grows out of its shaggy behind. The Chimera secretes deadly venom released through a bite and breathes fire.
When Bellerophon encounters the Chimera, it has the front and head of a male lion, the back of a dragon, and rattle snake for a tail, and goat head sticking out of its back which can spit fire and rotate all the way around and back. Percy Jackson says that monsters often change appearance to explain the differences.
The Chimera has many powers including:
- It can breathe fire.
- Its snake-headed tail has venomous fangs and excretes a venom that is acidic.
- It has human intelligence.
- It is immensely strong.
- In The Lightning Thief film, the part where Percy and his friends encounter Chimera and Echidna was replaced with them fighting the Hydra at a replica of the Parthenon in Tennessee. According to screen writer Craig Titley, the part was in his original script draft for the film, but was replaced with the Hydra scene due to the Chimera being deemed "too weird looking", and thus being seen as "un-relatable and unbelievable in its looks for an audience to connect to". Chris Columbus came up with the idea to replace the Chimera with the Hydra, as it was a more iconic creature that would also seem realistic for an audience to connect to. It was also supposedly easier for the actors to react to while filming. The scene itself was also thought to be too expensive and difficult to film. 
- In The Lightning Thief, Echidna calls the Chimera her son. However, in most ancient myths, the Chimera was a female, along with the fact that her name means 'she-goat.'
- In some myths the Chimera had dragon wings.
- Chimeras in botany are usually single organisms composed of two genetically different types of tissues. The word derived from the monster's name because of its several body part structure.
- In Paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal.
- For some myths, it has a knife in its body right after it bites its prey.