Astyanax is a genus of freshwater fish in the characin family (family Characidae) of order Characiformes. The type species is A. mexicanus, the Mexican tetra, and the roughly 100 Astyanax species are among the fishes known as tetras.

Astyanax is an adventure game for the Nintendo Entertainment System released in Japan in 1989 and elsewhere in 1990. Another game called The Astyanax was also released in arcades, and gameplay was very similar. Both the NES and arcade versions were known in Japan as Lord of King.