Who is Mulch Diggums from The Time Paradox and what is their importance?

Mulch Diggums is a dwarf. He is good friends with Holly and Artemis in the future, thus, it isn't a surprise that they should turn to him in the past. Mulch, however, has no idea that they will eventually become friends, but he is more than willing to help them out when he's promised a large cache of valuables to sell on the black market.