Tellos was an assault marine sergeant in the the space marine chapter known as the Soul Drinkers. He and his assault squad lead the attack on the Van Skorvold starfort. Under Sarpedon's command he fought threw the starfort to the soul spear, until it was stolen right in front of Sarpedon by tech-priests.
When the Soul Drinkers attacked the Mechanicus platform Tellos was fatally wounded with both his hands ripped off at the wrist by a tech-priest. Tellos would have been killed by the priest if Apothecary Pallas didn't come to his rescue and dragging him to safety.
While he was still recovering on the Soul Drinker ship called the Gundog Pallas found him jamming metal shafts in his stubbs. This was the beginning of the end for his sanity. Even after Pallas had removed the found new ones and stared destroying servitors in a library. During the Chapter Civil War Tellos was still on The Gundog and unable to fight. However soon after his mutations started.
Tellos had the most noticeable mutation second only to Sarpedon. So he could still fight (because he refused any other fate) he had a chain stuck into each stubb where his mutation of fast healing skin kept them in place. His second mutation was extreme muscle bulk which stretched his skin so anyone could see the massive bulk of muscle under his skin(He didn't wear anything from the waist up).
When Sarpedon was looking for the cure to stop their mutations form killing them and so they can start harvasting again Tellos disobeyed him many times. When they finally found the cures location the Soul Drinkers were force to leave Tellos and his forty assault marines behind on Stratix Luminae, last seen taking on tens of thousands of mutates and undead creatures from Teturact's army.
A few years later Sarpedon got word that Tellos and his Marines had killed every last thing on Stratix and pledged his loyalty to Knorne, the Chaos God of blood and war. Tellos was eventually tracked to Entymion IV were he and Sarpedon engaged in a titanic duel on a bridge. Sarpedon barely won but, when the were fighting in the water the bridge colasped on his buring him under the rubble. The Soul Drinkers left the planet and it was going to be destroyed due to it being over run with deamons and traitors. Tellos emerged from the ruins of the bridge and sat on a pile of freshly killed deamons who drew toclose to him. He watched as the exterminatus missiles bore into Entymion IV surface thinking More blood for the Blood God as the planet's core was blown up.