In the First Branch of the Mabinogi, Pwyll, king of Dyfed, puts himself into a debt of honour to Arawn, one of the two kings of the Otherworld, by rudely (and against the rules of royal etiquette) driving Arawn’s hounds – the hounds of another king, equal in honour – away from a cornered deer, and setting his own hounds upon it instead.
To erase the insult and gain Arawn’s friendship, Pwyll must take on Arawn’s appearance, and rule his kingdom in Annwn for a year and a day. At the end of this time, he must – in his guise of Arawn – fight and defeat the other king of Annwn: Hafgan.
The battle between the two kings is an recurring feature of the Celtic Otherworld. The King of Summer and the King of Winter meet in battle twice in each year. At Calan Gaeaf (Samhain), the Winter King in his youthful strength defeats the Summer King. At Calan Mai (Beltane), the battle goes the other way. Thus, the seasons progress, summer leading into winter, winter leading into summer. This is the meaning of the battle between Arawn and Hafgan.
In the First Branch, however, we learn that this eternal cycle has been broken. Arawn has worked out how to kill Hafgan forever, such that he cannot return to renew the battle. However, Arawn is apparently unable to do this himself: he is aware that he must act according to his role, and he is not able to vary his actions. However, Pwyll in his pride gives Arawn the opportunity to send a human in his place, wearing his face, to achieve what he himself cannot achieve.
Arawn, effectively, works out how to break the fourth wall and bring the audience into the drama.
Who is who, in this battle?
Arawn’s name does not tell us anything. Hafgan’s does.
‘Hafgan’ means “summer-born”.
Thus, in the Celtic conception of things, Hafgan is winter-conceived, summer-born; winter-mature, and summer-slain.
Hafgan is the winter god.
Pwyll, in Arawn’s form and according to Arawn’s instructions, strikes Hafgan a fatal blow – and refuses him the second strike that would grant him rebirth. Hafgan, recognising his doom, calls to his vassal lords, and tells them that he can no longer lead them. Without exception, they then pledge to follow Arawn, who is now the only king of Annwn.
Hafgan was the winter god.
Arawn was the summer god.
Now, thanks to his manipulation of Pwyll, Arawn is the sole ruler of Annwn.
And this is how the Celtic Otherworld became a land of eternal summer.