Due to his old age, Guld is looking for a replacement during the early portions of Link's quest. He wants to retire to a scenic land and escape the heat of Eldin Volcano.
After Link saves Eldin Volcano and allows the Mogmas to return home, Guld will agree to follow him to Pumpkin Landing. With the help of LD-301S Scrapper, Link brings Guld to the Lumpy Pumpkin where Kina is overjoyed and employs the Mogma to work plowing the pumpkin patch. Grateful, Kina gives Link five Gratitude Crystals.
Since many Mogmas are named after metals, his name is probably derived from the Swedish word "Guld" meaning gold, or else is simply derived from the English word.