Pyrrhus

Pyrrhus [Who2.com]:

Pyrrhus inherited the throne of Epirus in Northern Greece around 306 B.C.E., and as a young man proved himself on the battlefield again and again.

Pyrrhus apparently had great strategic skills, but he also had the reputation of not knowing when to stop. In 281 he went to Italy and defeated the Romans at Heraclea and Asculum, but suffered bitterly heavy losses.

The devastation led to his famous statement, "One more such victory and I am lost" -- hence the term "Pyrrhic victory" for any victory so costly as to be ruinous.