One of the original Greek myths of Heracles (note that there are many versions of the Greek myths).
Hercules came from a family of 4: His mother, the beautiful Alcmene; his father, Amphitryon; and his twin brother. His true father was Zeus, and so he was despised by Hera, the true wife of Zeus. So, he grew up with Amphitryon, his mother's husband and the father of his twin. Amphitryon was once in line for kingship of one of the biggest kingdoms in Greece, but after an accident he and Alcmene were exiled.
Heracles married and had several children, but one day in a rage he killed his entire family except his nephew, who hid. Some say he was inflected with madness by Hera, the true wife of Zeus, but he was still punished by having to serve 12 tasks for his cousin, the new king of the large kingdom his father set out to rule.
Heracles greatly disliked his cousin, and his cousin right back, so he gave him the twelve hardest, frustrating and low-down tasks. He was sent to kill or capture many monsters, and do many things besides. Yet Heracles kept coming back, gaining more fame each time.
Heracles remarried to a beautiful girl named Deianira. One day a centaur carried her off. Heracles killed the centaur, but before he could the centaur gave Deianira a love potion that was supposed to be rubbed on Heracles' clothes if she ever doubted his love.
Deianira used the potion a few years later, after Heracles went to war. It turns out Heracles was sacrificing prisoners of war to the gods. Halfway through the ritual, Heracles' skin started boiling. His shirt stuck to his skin. It turns out centaur blood was poisonus. The pain was so bad that Heracles begged to be burned so he could die in dignity. Deianira killed herself in guilt.
In the end, Zeus made Heracles a god as a reward of all the monsters he killed and the pain he had gone through. He was made immortal to guard the pillars of Heracles at where the Greeks thought all land ended.