Hercules (known as Heracles in Greece) is the mythical son of Zeus and Alcmene - although considered a hero in almost all the ancient myths, Hercules was actually a violent and brutal individual even by the standards of ancient Greece. Hercules is especially famous for his strength and this has remained his main focus in almost all media.
The story of Heracles starts as many stories of ancient Greece do, with a union between Zeus and a mortal woman. A man named Amphitryon, the grandson of the hero Perseus, another son of Zeus, had tried unsuccessfully to have a child with his wife Alchmene for several months before he was conscripted to fight in a war. In the end Amphitryon was drafted before he or Alchmene could tell if she was pregnant and he left swearing he would return to her. Amphitryon was wounded in battle and died of his injuries but with his dying breath he prayed to Zeus that his wife Alchmene would be safe and live to bare him a child. Zeus heard his great grandson's prayer and visited Alchmene that night disguised as Amphitryon. Zeus had relation's with Alchmene but left while Alchmene slept. Alchmene had no clue where her husband had gone but in a month's time received word that her husband had died in combat, leaving her to believe her night of passion with Amphitryon was just a vivid dream. However several months later Alchmene was surprised to find she as pregnant.
Alchmene bore a son and named him "Heracles," a reference to the goddess Hera, Zeus' wife, of whom Alchmene was a worshiper. Hera disliked the affairs of her husband and often punished the women who accepted his advances, in Alchmene's case she was unaware of it and besides was an avid worshiper of Hera so for perhaps this reason Hera spared Alchmene, she was unwilling to spare the child however and sent to serpents to devour Heracles while he was still in his cradle. Alchmene returned to the room to find the serpents about to kill her baby before Alchmene or the serpents could react Heracles grabbed and throttled the snakes and killed them with a simple grip, thrusting them about as if they were rattles. After the death of the snakes Alchmene and Hera both realized Heracles had phenomenal strength and Alchmene realized who it was that really came to her those nine month's prior.
Heracles would grow up using his strength to provide for his mother and hunt dangerous game for food, materials or money. Eventually Heracles met a woman named Megara, a princess of Thebes and the two fell in love. Megara invited Heracles to live in Thebes and the two settled down and had three children. Hera was never content to see Heracles living a simple carefree life and one day, in response to one of Zeus' other affairs, Hera took out her frustration on the adult Heracles. Hera placed Heracles under a spell and drove him to madness when he came home from a hunt one night, Heracles killed Megara and his children in his rage. By the mourning Heracles had come to his senses and was horrified at what he had done. Heracles could not bare to face Megara's father or the people of Thebes and ran off into the mountains in guilt and shame.
Over nebulous amount of time living in the wilderness Heracles came to the decision he had to seek forgiveness for his crimes to be free of his guilt. Heracles went to the Oracle of Delphi and asked what the gods would have of him to atone. The Oracle communed with the sun god Apollo and said Heracles must go to the city of Argos and speak with the king Eurystheus, who would test his resolve.
Heracles went Argos and sought out king Eurystheus, confessing his crime in the city's public forum and asking for some form of forgiveness. Eurystheus was considered a highly religious and spiritual king, unfortunately for Heracles though he was a devotee of Hera and communed with her over the situation. Hera told Eurystheus of many dangers that crept though the country side, many of them monsters that also served her. Eurystheus told Heracles he would need to complete no less than ten labours to be forgiven by the gods and so began the legendary Labous of Heracles. He ended up completing twelve labors total, two more than the required amount.
Hercules was quite happy to kill and although he was never a truly evil character he was in many ways a force of nature who could tear another man to shreds if it so suited him - this type of hero is common in mythology and despite what the modern age may think it is important to understand these cultural heroes are no less relevant and deserving of the title as they are, arguably, the ancestors of the superheroes and so forth we know today.