I'm 99.9% on the theory that Bran/The Three-Eyed Raven was the actual "Lord of Light". And it was the people who mistook his works for some kind of divine intervention.
We know the LoL was the Night King's opposite. Yet the Night King himself was obsessed with the Three-Eyed Raven.
The Night King was made under the Weirwood Tree, the same trees that the TER gets his power from.
The Night King can raise the dead into Wight Walkers. The LoL can raise the dead into Fire Wights (Jon, Beric, maybe even Melisandre)
IMO, I like that they left that up to discussion and interpretation. I personally dont need every detail of every show wrapped up with a bow and spoon fed to me. No fun in that.