Treasure of Tarmin is based off the game of the same name for the Intellivision.
Mattel's first Dungeons and Dragons game for the 2600 (see Tower of Mystery), Treasure of Tarmin is based off the game of the same name for the Intellivision. Strangely Mattel never attempted to port their first Intellivision D&D game Cloudy Mountain to the 2600 even though it was very popular and much simpler graphically (thus making for an easy port). Most people wouldn't have thought Treasure of Tarmin would be even remotely possible on the 2600, thankfully we were all pleasantly surprised.
Treasure of Tarmin was ported to the 2600 by Synth Corp., which was apparently just two guys working out of their garage in Chicago. Why Mattel chose (or even found) Synth Corp. is unknown, but these guys showed that they knew their stuff. Treasure of Tarmin is one of the most remarkable games on the 2600, showing that it could handle second generation games (albeit with blockier graphics).