Barntar is the farming god of the Rams.
Lights Going Out[]
Despite playing as a Ram clan, Barntar does not have a major role in Lights Going Out. He is, however, alluded to with the treasures Barntar's Plow, which rewards you a small amount of goods every time you successfully perform the Convert Pastures to Fields venture, and Barntar's Shovel, which makes the Restore Pastures venture more effective.
Worship[]
Barntar is not one of the gods your clan can worship, you cannot build any shrines or temples to him, and his worshipers cannot be put on the ring.
Other Stories[]
To read more on Barntar, see here on the Glorantha wiki.
Although not explicitly mentioned in this game, he is probably dead during Lights Going Out: in the lore of the various tabletop games, Vadrus was outlawed for murdering Barntar—the first act of kinstrife.
Barntar is a minor, but still actively worshiped, god in King of Dragon Pass, see here for more.