He was a mystic and necromancer of Callahorn.
He considered that he was meant to rule rather than serve fools who were below his genious, so he subtly and slyly subverted the rulers of the land in order to destroy the King Ruhl Buckhannah and his sons in order to rule himself. From a hidden room behind the throne room he heard the plans of the ruling family. He contacted the Warlock Lord Brona and declared his allegiance in return for the dark knowledge of necromancy. He was able to summon shades and control them according to his will. He intended to poison the king, make Palance accuse Balinor for this, and make Palance to kill himself for grief over his death.
When the Druid Allanon came to warn about Brona's return, Stenmin spoke against him, accusing him for being a troublemaker and a liar who sowed dissension for his own ends. Thus Allanon's warning went unheeded in the kingdom. Balinor Buckhannah however followed Allanon and Stenmin found the opportunity to manipulate Palance. When Ruhl went ill, Palance took over, and Stenmin flattered him that he was wiser and a better leader than his brother. He said that in a time of peace there was no need for the Border Patrol, which was just a tool of Balinor to overthrow him, and persuaded Palance to disband it. He also orchestrated the abduction of Shirl Ravenlock of Kern and accused Balinor for it, saying that he did not want Palance to have an heir.
When Balinor returned, he managed to have him imprisoned as a traitor. He learned that Hendel attempted to free Balinor and sent men to stop them.
When Menion Leah rescued Shirl and warned them of an incoming army, Stenmin thought that Menion was a danger to his plans and attampted to assassinate him in the middle of the night. Menion caught him and forced Stenmin to lead him to Balinor. Menion now recognized Stenmin as one of Shirl's kidnappers. Then Prince Palance came upon them; Stenmin failed to reassert his power of the prince and tried to ecape through the stone stairs, and slew the Palance who stood in his way with his dagger. Balinor ran after him, but Stenmin escaped to a hiding place within the palace.
During the end of the Third War of the Races, he led Brona's soldiers through passageways under Tyrsis.
Hendel protected Menion as he closed the trapdoor. He then saw Hendel fall; he wept and then looked up at Stenmin who tried to sneak out of the cellar. Menion grabbed Hendel's mace and slew Stenmin.
Although he had no reputation of being a mystic, this was revealed in the History of Tyrsis.
Jak Ohmsford and Shella Leah discovered his book locked in the library of Tyrsis, as well as the secret room behind the throne which he used to communicate with Brona. Using his own book, they used the Ritual of Summoning to bring Stenmin's shade the cause of the undead that ravage the city, and the magic flames that barred the Sword of Shannara. Stenmin would not cooperate, Jak threatened him with the Ritual of Shattering, and Stenmin was forced to reveal the Spell of Disruption.