That happened just as I was recruited for the Grey Wardens. He originally had another master, one who died due to darkspawn taint. Garahel had ingested some of it as well, but the kennel master thought I might be able to help him. He sent me after a flower with curative properties, and that was enough to save him, though he didn't join me right away.

Garahel was trying to find me ever since Ostagar was overrun, and I first saw him running toward me ahead of a darkspawn horde. He was trying to warn me, and the first thing he did after that was turn around to attack them. So brave.