His name is Bronzi. He is a treasure
Bronzi is first encountered in the Fire Sanctaury. He has been captured and chained to the ceiling, and will beg Link to free him, and promises Link a reward if he does. After Link rescues him, he attempts to run away without giving Link a gift, but after seeing that Link has the Mogma Mitts of his brother, Silva, he will realize that Link is most likely a friend of Silva, and will give him the Dungeon Map as well as a hint.
As many Mogmas' names are derived from minerals, it is likely that Bronzi comes from Bronze.