Short answers, pulled from the story.
Pyrrhus of Epirus entered the world in 319 BC within the rugged mountains of Epirus. His father Aeacides held only the title of prince while his mother Phthia was a Thessalian noblewoman and daughter of General Menon.
At Heraclea Consul Publius Valerius Laevinus led Roman forces against Pyrrhus's superior cavalry and deadly phalanx. Hieronymus of Cardia reported seven thousand Roman dead and three thousand Epirot losses including many officers.
During a confused battle within narrow city streets at Argos an old woman threw a tile that knocked Pyrrhus from his horse and broke part of his spine paralyzing him. Death was assured when Zopyrus beheaded the motionless body after the blow.
The term stems directly from statements made by Pyrrhus following the Battle of Asculum about future ruin. He reportedly stated that one more victory would utterly ruin them meaning a win costing so much it loses all worth.
Pyrrhus commanded armies numbering up to forty thousand troops throughout his career including twenty war elephants loaned by Ptolemy II Philadelphus. His force structure included elite bodyguard Companions Tarentine light horse Cretan mercenary archers and phalanx infantry maintaining deadly formations.