This river consisted of large streams of lava and magma and that flowed by the equatorial region and led to the Well of Darkness. In later years, King Hiss learnt that Evil-Lyn with the aid of Count Marzo intended to release Hordak from his prison in Despondos. This led to Hiss taking General Rattlor and two Snakemen to prevent Hordak's escape. As they neared the Well of Darkness, Evil-Lyn had cast the spell leading to Hiss bypassing the banks of the River of Fire and travelling on chunks of rock that flowed on top of the magma. There, Hiss battled He-Man who was under the mistaken belief that the Snakemen leader intended to conjure a dark plan at the Well of Darkness. Their skirmish led to portions of the wall by the River of Fire collapsing and seemingly killing King Hiss and Rattlor. However, the pair survived and intended to continue Hiss's plan for the conquest of Eternia.
- Presumably, it was formed when Hordak casted the Spell of Separation.