He was one of Tolkien's teachers at school. He drove Tolkien to Oxford for his first term at university (this was 1911, when car trips were still exotic). He advised Tolkien on getting a collection of poetry published (it didn't happen). Some years later, Tolkien sent him what became The Lays of Beleriand to read and comment on, and, to provide context, wrote "A Sketch of the Mythology" which was the seed out of which came all subsequent versions of the Silmarillion.
Here's his unexpectedly surprising biography.