Three entries with the name Amangon.
Amangon
Amagons, Amangons, Amaugon
A king in Arthur’s service in Renaut de Bâgé’s Le Bel Inconnu, probably from Chrétien’s Amauguin.
He suggested a tournament at the Castle of Maidens when Arthur wanted to lure Guinglain, the son of Gawain, back to court.
Amangon is also mentioned briefly in La Bataille de Loquifer and Les Merveilles de Rigomer.
Source
Le Bel Inconnu | Renaut de Bâgé, 1185-1190
La Bataille de Loquifer | c. 1230
Amangon
A wicked king who ravaged a collection of well fairies who lived in the Grail Kingdom, stealing their golden cups. Other knights followed his example. Afterwards, the kingdom became a waste land, and the Grail Castle was hidden.
Amangon had a son named Pecorins.
See also
Fairies | Myths and Legends
Source
The Elucidation | 13th century
Amangon
The King of Greenland and father of Guenloie, Gawain’s love, in Meriadeuc. He served Arthur.
He is also named as the ruler of the Land From Which No One Returns. This according to the Old French Le Chevalier as deus espées.
Source
Meriadeuc or Le Chevalier aux Deux Éspées | c. 1225-1250