Neville is a guardian and one of Ren's wolves, firstly in the Bane pack and later in the somewhat-formed Haldis pack. He likes (and is talented in) poetry and singing, and sings at the Burnout, which later turns out to be run by searchers.
He's Mason's boyfriend and they share a happy relationship, which is challenged during the first book due to the fact that the Keepers wouldn't approve, likely because they would be unable to have children to help continue the yet-to-form Haldis pack, which would likely be pretty tiny, and because to begin with Mason is in a rival pack, the Nightshades. Despite this, they stay together for the entire series. Whilst Calla doesn't find out about their relationship until partially into the book (after Ansel informs her) it is suggested that it's been going on for quite a long time, or at the very least -and with certainty- before the beginning of the book series.