Griswold is the
blacksmith of
Tristram, the town in the first
Diablo. He's a friendly fellow, but will still charge you for any equipment repairs you need him to do. He also sells a wide variety of randomly generated normal and magic items (based on your
character level), and is involved in various
quests.
Griswold was one of the few survivors of the the ill-faited raid on the
Labrynth. This raid was led by
Lazarus, who, though once a holy power of
Zakarum, was by that time corrupted and enslaved by
Diablo. Supposedly, the raid happened just a few weeks/months before you arrived; now Griswold is a broken man and no longer has the will to venture into the depths (similar to
Farnham).
Spoiler Alert (read at your own risk):
In Diablo II, when you revisit Tristram to rescue Cain, Griswold makes a surprise appearance. This time, however, he is a zombie; fully under the power of Diablo/Andariel. He's the hardest monster in the area, and is surrounded by other boss-monsters and their minions. When you slay him, he'll drop a nice prize.