Skeletons are the remains of a creature given life through magic or the blessing of the Crowned Death, a Dark God. Most of them are unintelligent and suited only as foot soldiers and unskilled labor. Exceptions appear to be those creatures who are favored by Crowned Death, who seem to keep the intelligence, skills and maybe memories from when they were alive so that they can better serve him.
All known skeletons to date who were not made to do otherwise (ex. Keeper Zarekos making most his skeleton minion worship him, in a temple built in his own honor) worship Crowned Death. Skeletons do not need to eat, drink, breathe or remain in one piece to keep functioning.
Most notable are the cleric-sorcerers who make up the death god's clergy, the Death Priests. Wearing deep purple robes adorned with the skulls of dead beasts, and carrying the mighty and dreaded Battle-Staves of Calarine, they are incredibly dangerous combatants.