Elmus is a Nord former resident of the Thirsk Mead Hall who can initially be found at Bujold's Retreat, along with the other outcasts. Elmus will move back into the hall if the Dragonborn agrees to help Bujold take the hall back from the rieklings.
Elmus, along with the other Thirsk warriors, will aid in killing the rieklings in the Thirsk Mead Hall, and will move back into the hall after it is taken.
The Riekling Chief asks the Dragonborn to kill the Nords at Bujold's Retreat.
After asking he if there is anything the Dragonborn can do to make life in exile any better while at Bujold's Retreat, Elmus asks the Dragonborn to retrieve one bottle of ashfire mead from Thirsk Mead Hall.
After taking the hall back, Elmus will ask the Dragonborn to gather one sample of juniper berries, after Elmus is asked about how the mead production is going.