Ok, the actual name is Warrior of Sunlight. Though he doesn't come right out and say it, I always figured Solaire was a Sunbro. He's either a Sunbro or in the Princess Guard. I doubt the latter though, since it's an option for him to help you kill her guards. There were not NPC Sunbros in DS2, no. Unless I missed someone, not sure. Solaire was just unique to me in his story in the game and being available as a summon.
It just saddens me that they've made it no real reason to be a sunbro anymore. I mean unless you want the particular rewards from offering Sunlight Medals, but I still find rewards from helping in other covenants better.