The "Ördög" or "Urdung" is one of the main dieties of the Pre-Christian Hungarian shamanic religion. Due to the rapid conversion to Christianity in the 9th and the 10th century, and the lack of written records from the Pre-Christian era of Hungarain history, there are only very limited data left about the beliefs of the pagan Hungarians.
The Ördög was the king of the Pokol (underworld in the pagan Hungarian mythology), a dark diety, who often walked the Earth. In the old myths the Ördög often appeared as a fox, dark flame, or as a Hungarian sheperd with completely black eyeballs. He had the habit to make bets with mortals, promosing wonderful rewards in order to corrupt them. If he lost the bet however, he always granted what he promised.
He also appears in the tales where the protagonist is dying, or in serious trouble. The Ördög appears, introduces himself, and offers help. If the offer is accepted, the Ördög saves the protagonist, and tells him that one day he will knock on his/her door, and will ask something in return for the help. In these tales the Ördög shows up years later, and claims the protagonist's first born son. The Ördög also took bad people down to the Pokol where he cooked them in a giant cauldron and ate them.
These stories, although they originate from much earlier than the 9th century, are sill remembered in the 21th century, as debtime stories for children. Hungarians still say when they are angry at someone that; "Az Ördög vigyen el!" which means "I wish the Ördög took you!"
Those boys the Ördög actually took in the myths are the "Ördögfi" (Ördög's son). They are nasty, rebellious creatures, appearing as a young male (almost aways Hungarians) causing troubles. In the tales they often are imrisoned for theft of vandlizing properties, and they promise the protagonist that if he/she frees them their father will reward him/her.
Since the Ördög was a dark, shady character in these folk tales, the first Hungarian-speaking missionaries in the 9th and 10th century used his name referring to the Christian "Devil". Due to their activity, the words "Ördög" and "Pokol" are still used, meaning the "Devil" and "Hell".
The word "Ördög" also meant various evil things in Hungarian mythology such as the "Lidérc" or even the "Vámpír" - "Vampire" in English.