Thoth was one of Apep's original three Underlords, along with Ra and Nut. Despite the formal title of "underlord," in these ancient times this was the equivalent of what would now be known as a System Lord. Indeed, modern history records him as having the rank of System Lord.
Thoth was the original Goa'uld scientist, and is credited with the creation of the first rudimentary sarcophagus. This primitive, yet powerful, device exerted a heavy toll on Goa'uld symbiotes, and was responsible for introducing naquadah into the biology of the Goa'uld species. Thoth was known in legend as the Scribe of the Gods, and he supposedly recorded his wisdom in the Book of Thoth.
Thoth apparently allied with Anubis in his rebellion against the rest of the System Lords. After Anubis murdered Apep and was defeated in a century-long war, he and Thoth were both exiled and stripped of the rank of System Lord. He became a prominent scientist under Anubis during his exile. Much later, during Anubis's return, he was in charge of the Kull Warriors’ genetic engineering and maintenance and also worked on the Telchak device research. However, he was unable to find a fatal flaw in the genetic makeup of the Kulls’ symbiote. Thoth was killed by SG-1 when he found them in the control room on Tartarus. (SG1: "Evolution, Part 2")
- Like many underlords, Thoth has been seen using a silver hand device.
- Thoth is expressly identified as a fully-fledged System Lord in the RPG book Roleplaying Game