From Guild of Archivists

Rijus was Gehn's serving man, who was very tall and strong, had a large, domed head that looked as if it was made of polished ivory, and had seemingly lidless eyes. He was mute, but he understood Gehn's orders and he somehow knew his way around K'veer. His familiarity with K'veer suggests that he was a D'ni survivor, indeed the ending -us is seen also in D'ni names like Ventus, Neferus, Andritus, and Aitrus (and perhaps Atrus and even Sirrus); however it's also possible that he was one of the native slaves of Gehn's Ages, taken by him as a personal servant.

When Atrus attempted to escape from Gehn to return to the Cleft, Rijus found an ancient boat for Gehn to pursue him with.

Nothing is known about Rijus's life before Atrus's first arrival in D'ni and after Atrus's imprisonment in the K'veer chamber. However, it has been speculated that Rijus is the same person referred to as Corlam in the Book of Ti'ana, who was A'gaeris' mute assistant, however there has been nothing to definitively prove or disprove this theory.