Who is Mim from Unfinished Tales of Numenor and Middle-earth and what is their importance?

Mim is a dwarf that Turin comes across during his travels. Mim and his two sons are scavenging when Turin and his men come across them. Turin and his men stop him from following his sons and, as a result, one of his sons dies during the night. Mim still holds up his end of the bargain, but he refuses to feed the outlaws who were part of the attack on his son.