Severian Marcella, a grey-haired man, was arguably the second most important figure in the founding of Seleucar. He shared a childhood in Thera with Nikolas and often bullied him into giving up food - an act he admitted later on with shame. Years later, he accompanied Nikolas on his travels, providing a cynical foil to Nikolas' lofty optimism, and engaged him in such debates as the so-called "Sermon on the Rocks." Eventually, he gave in to Nikolas' idealism, and when the young man became Nicator and his burgeoning village branched into a bustling capital, Severian was appointed as the duke and later chancellor of Seleucar - the right hand of Emperor Nicator himself. He outlived Nicator, but passed away mere years before the War of the Deeps came to fulfil the prophecy of the Black Wave.
The Marcella Library on Kephry Park Road in southern Seleucar was named in his honour.
Severian once assisted with the Trial of Rebirth on the plane of Ceylon by teaching new adventurers basic knowledge about themselves and others.
Severian's likeness is inscribed upon a mystical card, inspired by his perspicacious preparation of Seleucar against the Tsol'teth onslaught.