THE CHIMAERA

She was of divine race, not of men, in the fore part a lion, in the hinder a serpent, and in the middle a goat, breathing forth in terrible manner the force of blazing fire. And Bellerophon slew her, trusting the signs of the gods.
Homer, Iliad 6.181

The Chimaera who breathed raging fire, a creature fearful, great, swift footed and strong, who had three heads, one of grim-eyed lion, another of a goat, and another of a serpent. In her forepart she was a lion; in her hinderpart a dragon; and in her middle part, a goat, breathing forth a fearful blast of blazing fire. Her did Pegasus and noble Bellerophon slay.
Hesiod, Theogony 319

The Chimaera was a fire-breathing she-goat with the head of a lion, the body of a goat and a serpent's tail. This unlikely beast was the product of a union between the equally hideous monsters Typhon and Echidne.

Echidne bore a particularly dreadful brood to Typhon: along with the Chimaera, the two of them produced Cerberus, the three-headed hound of Hades; Orthrus, the two-headed hound of Geryon; the Sphinx, who had a woman's head, lion's body, serpent's tail, and eagle's wings; and the Hydra, a multi-headed water serpent. The Chimaera and her siblings comprised some of the most feared monsters in Greek mythology.

(It should be noted that in some versions of the Sphinx story, it is suggested that its parents were the Chimaera and Orthrus.)

This dreaded monster took up residence in a place called Lycia and caused great havoc, killing and terrorizing all the neighboring area. In due time, the hero called Bellerophon, riding the winged horse Pegasus, challenged this beast.

Illustration from Tanglewood Tales, c. 1920

Flying above the Chimaera on Pegasus, Bellerophon rained down arrows on the creature, with little effect - the beast was too strong and threatened to overwhelm the hero with its flaming breath. Bellerophon then attached a lump of lead to the point of his spear and thrust it between the Chimaera's jaws. The creature's fiery breath melted the lead, which trickled down its throat, burning its insides and instantly killing it.

After overcoming the Chimaera, Bellerophon defeated the neighboring enemies, including the fierce nation of women warriors called the Amazons, and eventually became the champion of Lycia. However, he was doomed to a bad ending, as you'll see when you check out the Bellerophon page...

The Chimaera of Arezzo

The Chimaera of Arezzo is a bronze statue which was found in Arezzo, Italy, in the year 1553. It is of Etruscan origin, probably from 5th century BC, and it's one of the most beautiful existing examples of ancient mythological art. It is presently housed at the Archeological museum in Firenze, Italy.

...in a certain country of Asia, a terrible monster, called a Chimaera, had made its appearance, and was doing more mischief than could be talked about between now and sunset. According to the best accounts which I have been able to obtain, this Chimaera was nearly, if not quite, the ugliest and most poisonous creature, and the strangest and unaccountablest, and the hardest to fight with, and the most difficult to run away from, that ever came out of the earth's inside. It had a tail like a boa-constrictor; its body was like I do not care what; and it had three separate heads, one of which was a lion's, the second a goat's, and the third an abominably great snake's. And a hot blast of fire came flaming out of each of its three mouths! Being an earthly monster, I doubt whether it had any wings; but, wings or no, it ran like a goat and a lion, and wriggled along like a serpent, and thus contrived to make about as much speed as all the three together.
Nathaniel Hawthorne, "A Wonder-Book for Girls and Boys", 1852

It had the fore part of a lion, the tail of a dragon, and its third head, the middle one, was that of a goat, through which it belched fire. And it devastated the country and harried the cattle; for it was a single creature with the power of three beasts. It is said, too, that this Chimera was bred by Amisodarus, as Homer affirms, or that it was begotten by Typhon on Echidna, as Hesiod relates. So Bellerophon mounted his winged steed Pegasus, offspring of Medusa and Poseidon, and soaring on high shot down the Chimera from above.
Pseudo-Apollodorus, Library 1.151