Mathias Thunderheart was the son of a military tactician in Scarsdale, and he was enlisted in an arcane military academy at a young age. From then on, he honed his innate magical abilities to rain destruction down on his enemies.
Mathias originally traveled to Tethyamar to seek out knowledge about the rumored Temple of the Unknown, later to be revealed as a Temple of Ao. After joining the Party and assisting them in successfully liberating Tethyamar from the chokehold of Lionel Mountebank, Mathias was shockingly assassinated by Ravinder Nath. However, instead of dying, his soul was trapped by a phylactery that happened to be in the possession of Darian Skullbasher.
Experimentation and concentration eventually allowed Mathias to access his arcane powers even while within the phylactery and use them to help the party in combat. Other abilities such as telepathy were also utilized.
Eventually, the Party traveled to Mystra’s holiest temple and fought their way through its labyrinth to gain access to the Garden of Life. There, the Party witnessed the rebirth of Mathias in his current Warforged body after offering an arrowhead as the material from which his new body should be created.