The threefold death, which is suffered by kings, heroes, and gods, is a putatively Proto-Indo-European theme, reconstructed from medieval accounts of Celtic and Germanic mythology and archaeologically attested from ancient bodies such as Lindow Man.
Some proponents of the trifunctional hypothesis distinguish two types of threefold deaths in Indo-European myth and ritual. In the first type of threefold death, one person dies simultaneously in three ways. He dies by hanging (or strangulation or falling from a tree), by drowning (or poison), and by wounding. These three deaths are foretold, and are often punishment for an offense against the three functions of Indo-European society. The second form of the threefold death is split into three distinct parts; these distinct deaths are sacrifices to three distinct gods of the three functions.
In Welsh legend, Myrddin Wyllt (one of the sources for Merlin of Arthurian legend) is associated with threefold death. As a test of his skill, Merlin is asked to prophesy how a boy will die. He says the boy will fall from a rock. The same boy, with a change of clothes, is presented again, and Merlin prophesies that he will hang. Then, dressed in a girl's clothes, the boy is presented, and Merlin replies, "Woman or no, he will drown." As a young man, the victim, in a hunt, falls from a rock, is caught in a tree, and hanging head down in a lake, drowns.
Myrddin Wyllt also reportedly prophesied his own death, which would happen by falling, stabbing, and drowning. This was fulfilled when a gang of jeering shepherds drove him off a cliff, where he was impaled on a stake left by fishermen, and died with his head below water.
The Norse god Odin is also associated with the threefold death. Human sacrifices to Odin were hanged from trees. Odin is said to have hanged himself in order to learn the secrets of magic.
One of the most prominent examples of this threefold death in three separate sacrifices comes to us from Lucan In his epic poem, Pharsalia, which relates Caesar's conquest of Gaul, he describes a set of three Celtic gods who receive human sacrifices: et quibus inmitis placatur sanguine diro/ Teutates horrensque feris altaribus Esus/ et Taranis Scythicae non mitior ara Dianae. ("To whom they appease with cruel blood, harsh Teutates, and wild, bristling Esus, and Taranis whose altar is as insatiable as that of Scythian Diana.")