The Sirens are characters from The Twelve Tasks of Asterix. They are led by a high priestess with long, black hair (who is voiced by Micheline Dax in the French version of the film), suggesting that they follow a religious hierarchy.
The Sirens are beautiful women with enchanting voices. They dwell on the Isle of Pleasure, which sits in the middle of a lake that Asterix and Obelix must cross to complete their fourth task. They lure the Gauls to the island and try to seduce them, but Obelix is less interested in the Sirens' company than he is in eating a nice wild boar. He becomes frustrated when he learns that there are no wild boars on the Isle of Pleasure, and gets in a dispute that ends with the Sirens kicking him off the island. The high priestess tries to seduce Asterix instead, but he, too, leaves the island when Obelix calls to him.
At the end of the film, Caius Tiddlus is seen enjoying himself with some Sirens on the Isle of Pleasure.