Orthros was a two-headed dog born to Greek mythology's most famous monster parents, Typhon and Echidna. 

Mythology tells us extremely little about this potentially fascinating beast whose sole purpose in myth seemed to be getting unceremoniously slain by the jerk/hero Hercules.

To be specific, Orthros was essentially the cattle dog for Geryon, the three-bodied giant who was king of Erytheia, the sunset isle. Orthros worked beside a cattle herder named Eurytion and together they watched over Geryon's herd of magnificent red cattle.

Not a bad life for a monster, really. Maybe a little too cushy. One day, Hercules comes by to swipe the cattle and clubs Orthros in the head. Everyone dies. Hercules wins. Sadly, there isn't much more to say than that. The dog just can't have his day. He was a two-headed monster dog, which would be impressive, except his brother is Cerberus, the three-headed monster dog. I mean, seriously, the guy can't win.