The Demolitionist is another NPC in Terraria. He seems to resemble dwarves, possible why "Gimli" is a possible name for the Demolitionist. Demolitionists will sell explosives and sometimes other projectiles.
The mining helmet can be removed and reused as a mining helmet in which is sold by the Merchant.
For more information, click <a href=http://terraria.gamepedia.com/Demolitionist>here.
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