Cephalon Samodeus is an obscure character who is the creator of the Riven mods. In-game, he appears during the Riven selection screen when re-rolling the stats of a Riven mod with kuva, but has no dialogue. In the leadup to The War Within update (Update 19), a teaser site was released which contains some cryptic text from Samodeus, which composes the entirety of his lore.
You are either extremely lucky or a thieving wench. You probably don't even appreciate what you have now. My life. My soul. My art. You will need to prove yourself before I reveal the beauty within this work.
Until now, you've ignorantly used my creations for whatever suits you, but this is only a taste of what I have accomplished. For now, you can nest my beautiful creations inside your crude rifle like a sad philistine until you understand the depths of my unique creations.
The first thing you must learn is that each piece of my grand creation is malleable and unique. Each piece is both solitary and part of my fractured self. Do you understand? I fear I may have overwhelmed you already. To begin, I'll limit you to a dozen and three, but you'll quickly see the vast array of hidden possibilities, both rapturous and unfavourable. Now, leave me be and return here when you can share what my art has shown you.
This text was especially cryptic before the existence of Riven mods was revealed, and references the initial Riven capacity limit of 15.
On 09 November 2018, with Update 24 and the release of Fortuna, Riven mod dispositions were rebalanced. With this first major readjustment of the disposition values, each Tenno was sent an inbox message from Cephalon Samodeus.
Riven Disposition Changes
My beautiful creations (which you know as Riven mods) were beginning to bore me, so I've reconfigured certain parameters to make my art truly shine. Be cautious when engaging in your crude Tenno bartering, as some mods may not be as they once were.
This is so far the only in-game acknowledgement that such a character exists.