Lion of Cithaeron

The Lion of Cithaeron was a lion in Greek mythology which was harassing the lands of king Amphitryon and king Thespius or of king Megareus. According to the Suda, it was also called Thespian lion and ravine lion (Χαραδραῖος λέων) because it lived in a place called "Ravine" (χαράδρα). Some myths say that it was killed by Herakles, while others by Alcathous or by the god Apollo.

Herakles
One account of the myth is that king Thespius asked Herakles to kill the lion. Herakles hunted it for fifty days and finally killed it. During each night of the hunt Heracles slept with each of the fifty daughters of the king, who in turn each gave birth to a son. After he slew the animal, Herakles dressed himself in the skin of the animal and wore the scalp as a helmet. According to the Suda it was killed near Thespiae. Herakles killed the lion while he was eighteen years old, and before killing the Nemean lion.

Alcathous
While another myth say that the lion was killed by Alcathous.

The lion had killed many including Euippus, a son of the king of Megara Megareus. The king promised that he who would kill the Cithaeronian lion would marry his daughter Evaechme and succeed him in the throne. Alcathous killed the lion and when he became the king, he built the sanctuary of Artemis Agrotera (Huntress) (Ἀγροτέραν Ἄρτεμιν) and Apollo Agraeus (Hunter) (Ἀπόλλωνα Ἀγραῖον).

Apollo
Another myth say that the lion was killed by the god Apollo.

Because the god killed the lion, he was called Agraeus (Hunter) and Alcathous erected a temple for him at Megara under the name of Apollo Agraeus.