(Robert John) Wace (c. 1100 - c. 1174) was an Anglo-Norman poet, who was born in Jersey and brought up in mainland Normandy. Roman de Brut (c. 1155) was based on the Historia Regum Britanniae of Geoffrey of Monmouth. Its popularity is explained by the new accessibility to a wider public of the Arthur legend in a vernacular language. Wace was the first to mention the legend of King Arthur's Round Table and ascribe the name Excalibur to Arthur's sword, although he on the whole adds only minor details to Geoffrey's text. The Roman de Brut became the basis, in turn, for Layamon's Brut, an alliterative Middle English poem, and Piers Langtoft's Chronicle. His extant works include: Roman de Rou (c. 1174) - a verse history of the Dukes of Normandy. Other works, also in verse, include lives of Saint Margaret and Saint Nicholas.
It's been a while since I read these. I remember liking one much more than the other. One of them leans very hard into Arthur being a violent warlord. The other is more interested in courtly love. It's still a few centuries before Mallory's Morte de Arthur and you can tell that he had a lot of work to do. But interesting comparing the two and then comparing this against Monmouth's Historium Regnum. In both I thought it very strange how much they emphasized that Arthur was Roman over his being British. I don't know if this was supposed to be an attack on Rome/the Catholic Church at the time or why the writers thought that this would somehow cement Arthur's legitimacy. It is curious.
These are the works of a couple of poets, who sought to write down the Arthurian tales that had become popular in the centuries after the Norman invasion of England. As such, they're probably the best source documents we have.
Full of unlikely events, magic, and mythical creatures they're a good insight into the medieval European mind. It's easy to forget how very dark the darkness of night was before the coming of gas and electricity; impossible to understand how dark the medieval mind was before science. What hope was there against foreign invaders? Somewhere in the mists there had to be a mythical hero.