Rivalen Tanthul

Rivalen Tanthul was one of the twelve Princes of Shade. Rivalen was an accomplished wizard but also The Nightseer, a high priest of Shar, the goddess of loss and night. This made him what the Netheril call a Theurge, blending the magic of the Art and the Power. Rivalen was Hadrhune's greatest rival. He resented the approval that his father had shown to Hadrhune, and was secretly working to undermine him. He knew he must exercise great caution, because Hadrhune's enemies had an unsettling tendency of disappearing.

Although High Prince Telamont is the temporal ruler of the Shadovars, Prince Rivalen was their spiritual leader. From the enormous Hall of Shadow located near the royal palace, the prince administered Shar's clergy and pronounced her will to the faithful.

In Forgotten Realms
In -365 DR, Rivalen killed his mother Alashar by command of Shar. In 1372 DR, Rivalen's divinations enabled his father, Telamont Tanthul, to finally guide Shade back to Faerûn. Shortly after, Rivalen fought Galaeron Nihmedu and Vangerdahast at the battle of Tilverton. In 1374 DR, Rivalen orchestrated, with the help of his brother Brennus, the takeover of the land of Sembia and its reduction to a vassal state of the City of Shade. Rivalen then became a demigod/exarch, having absorbed a shard of Mask's power after helping Erevis Cale and Drasek Riven kill Kesson Rel.

In 1484 DR, Vasen and Erevis Cale stripped Rivalen, Riven and Mephistopheles of their divinity before Rivalen could finish the Cycle of Night so that Shar could annihilate the world. Mask subsequently reincarnated in Riven and the Cycle of Night was finally stopped. Rivalen died along with Brennus when Sakkors fell upon Ordulin while his brother held him down, avenging his mother Alashar.

In LOTM: Witnesses of Sleepy Hollow
Rivalen Tanthul is set to appear in LOTM: Witnesses of Sleepy Hollow as the primary antagonist of its upcoming Netherese Darkness spinoff.