Lord of the sky, the rain god. His weapon is a thunderbolt he hurls at his enemies.
One of the Olympian gods, Zeus defeated and imprisoned his father Cronus (a Titan) in the Tartarus realm, guarded by Tartarus doors, and then drew lots with his brothers Poseidon and Hades to see who would become the supreme ruler of the gods. Zeus won the draw and became the ruler of the gods. He is married to Hera but his many affairs are a well known fact.
In Greek mythology is represented to be armed with lightnings, often prepared by Hephaestus, his son.
Lord of the underworld, ruler of the dead and is also known as the god of wealth.
In Greek mythology Hades' identifying possessions included a famed helmet of darkness, given to him by the Cyclopes, which made anyone who wore it invisible. In the movie, Hades wears no such helmet.
Mortals' Passage to the Underworld When men burned their dead (Greek tradition), they placed two drachmas underneath the deceased's tongue to pay for passage through the River Styx and reach the underworld.
Erebus, the Kingdom of Hades, is guarded by Cerberus, the three headed dog of the underworld. Cerberus is represented in the 1981 film as a two headed dog guarding Medusa's lair.
Lord of the seas and oceans, also know as the "Earthshaker."
Poseidon is Zeus's brother and claimed the sea when drawing lots between his brothers to see who would rule which section of the world. Poseidon drew the kingdom of water and was given control over the shores, oceans, seas and rivers. Men often had to pray for Poseidon's favor in order to have good weather in their travels.
Poseidon is represented with a golden trident, and just like Hades's helmet and Zeus's thunderbolt, it is a gift from the Cyclops, who were great smiths.
Medusa began life as a girl so lovely she made Athena jealous. Such beauty turned Poseidon's head. He seduced the girl but, unfortunately for her did so in one of Athena's temples. So Medusa was turned by Athena into a Gorgon. Since she started as human she remained mortal, and Athena later helped Perseus kill her.
In original Greek Mythology, Perseus does kill her, but there are several versions of how he killed her, the most famous is the one showed in both movies: he kills her by cutting her head off, others and less violent say that he made Medusa to look herself thanks to a mirror, the god Hermes (not shown in the movie) gives him a drink that allows him to survive Medusa's magical power of turning everyone into stone, and so he was able to accomplish his goal, the encounter with Hermes is only told in the second version of the story.
A Gorgon is a female monster with snakes for hair, their faces so ugly that anyone who sees them will turn to stone. There were three Gorgons, two were born and were immortal. Medusa was turned into a Gorgon by Athena, and therefore was not immortal.
Originally this creature did not come from Greek tradition, nor Roman for that matter. In the Greek myths, Perseus faced the Cetus, a sea serpent. The Kraken came from the myths or sagas of the Norse, more than a thousand years after the Greeks. The Kraken is a legendary creature that resembled a giant squid and was known for destroying ships. Its tremendous size and power is to be matched with that of a titan, and the gods often refer to him as the last of the Titans, which is ironic because the Titans are immortal. In his physical state we can tell that he is a marine creature, also capable of breathing air. In the 1981 movie, this one is kept jailed in the profound of the seas, guarded by Poseidon. Hades is now the guard of this adversary to Perseus in the 2010 remake.
Originally the offspring of Gaia (the Earth-mother) and Ouranos (the Sky-father) and were the first race of divine beings. Kronos and Rhea produced the first generation of Olympians whom Kronos, out of fear of being overthrown, then decided to eat all his children. Rhea fearing for her last child, Zeus, fed Kronos a wrapped up rock. Grownup Zeus killed Kronos and freed his siblings from Kronos stomach. At first the relationship between the Olympians and Titans were relatively amicable, but eventually the Titanomachy, the war against the Titans, broke out, in which the Titans were finally subdued and punished.
Today the word has come to refer to something huge. Therefore, even though there aren't any literal titans (neither Medusa, nor the Kraken, or Cetus, were titans; they were merely monsters) in either the Clash of the Titans films, the title presumably refers to a clash of titanic figures, e.g. Perseus and Medusa, Medusa and the Kraken, etc.
Perseus was a son of Zeus. His mother Danae was locked in a prison by her own father, King Acrisius of Argos. The King had been told that his daughter's son would one day kill him. Instead of taking the risk that his daughter would become pregnant, he locked her away in a tower with no doors and only one small window. Zeus turned himself into a shower of gold and slipped through the window. He turned the prison into a lovely meadow filled with sun. Danae's father saw light coming from the window and demanded that a wall be torn down so he could check on his daughter.
When the wall came down Danae could be seen holding a baby boy. Mother and child were put in a chest and shoved into the ocean with the hopes that they would perish. They washed up on the shore of an island and were greeted by Dictys (a fisherman). Perseus grew up quite happily until one day King Polydectes decided he wanted to marry Perseus' mother.
Danae was not interested in marrying the king, however he wasn't taking no for an answer, but she had Perseus to protect her. The King couldn't get around Perseus, so instead he pretended to marry someone else. When Perseus came to the wedding without a gift (he couldn't afford one) the King demanded Perseus bring him Medusa's head as a gift.
Perseus went on a long quest, ended up slaying Medusa (the Gorgon) and on his way back to the king, uses the head to free Princess Andromeda, accidentally kills his grandfather (which means the prophecy did come true despite the old kings efforts), takes the head back to King Polydectes only to find out the wedding was a sham and that his mother has been forced to be the King's servant. Perseus was so upset by this that he used Medusa's head to turn his enemies in the Kingdom to stone, thereby rescuing his mother.
Much much later Perseus and Andromeda are placed into the sky as constellations.
In the 2010 movie, Perseus' mother dies in the chest. Perseus kills Medusa to help him kill the Kraken. Perseus kills the Kraken using Medusa's head.
In Greek Mythology, the Pegasus was originally made by Poseidon, in which he was first considered to be a horse-god type, but it was foaled by blood of the Gorgon, Medusa when the demi-god Persus killed her. He originally was ridden by Bellerophon, another Greek hero, unlike in the movies, in which Pegasus belonged to Zeus and it is ridden by Perseus. In Clash of the Titans Pegasus's coat is black, though usually portrayed pure white. In additon, the Greek myths state that there is only one Pegasus, but in the film there is a flock of winged horses when Io first informs Perseus of the Pegasus.
In Greek Mythology, Cerberus guards the entrance to the Underworld instead of Medusa's lair, and has originally three heads, unlike the movie in which has only two and its size is smaller than the original one.
Also, the Cerberus dog was capture in Greek mythology by the demigod hero Heracles as his last labor, instead of Perseus as the movie shows in the 1981 movie.