Io is a figure in Greek mythology, one of the mortal lovers of Zeus. Her descendants include Hercules and Perseus. There is a moon of Jupiter named after her. Most prominently though, Io is an Amazon weaponsmith with an unrequited love for Wonder Woman.
The mythical Io was first adapted (albeit erroneously) in Hawkman (Volume 3) #16 (1995). The Amazon smith was created by Greg Rucka and Drew Johnson, first appearing in Wonder Woman (Volume 2) #196.