Timaias Adama, Sage of the Endless Sword, is also called The Sword Sage. He is a backstory character of some importance to the entire Cradle series, and especially to Yerin Arelius. The most information about the Sage is found in book 1, Unsouled and in book 8, Wintersteel, in the prologue. There is a little more info about him in book 10, Reaper. See also Path of the Endless Sword
The Sage of the Endless Sword was Yerin’s beloved master until he was murdered when she was about 16 or 17 years old (Unsouled). He adopted her and taught her the Path of the Endless Sword. He rescued her in childhood, directly after her entire world stopped when the Dreadgod Bleeding Phoenix passed over her village, pursued by murderous acolytes from Redmoon Hall, one of the Dreadgod Cults
The Sword Sage was elite, highly respected and skilled, and yet a kind and wise master. He loved young Yerin, even though it wasn’t his way to be flowery or expressive about it. He gave her a steelborn Iron body when she was younger. He died trying to find information about how to remove a Blood Shadow from her without harming her spirit.
From the first time Eithan Arelius sees heartbroken Yerin in book 2, his internal opinions of her deceased master are always high. He wants to do well by the man, and continue the good work the Sage began. He adopts her and continues her training, and helps her understand her Blood Shadow, who becomes known as Ruby.
His Fiancée, Min Shuei
The Sage was betrothed to Min Shuei the Winter Sage, who made his wintersteel sword, the Endless Sword. She mentored Yerin during the Uncrowned Tournament, along with the Akura Sage, Akura Charity. Min Shuei first revealed his personal name (Adama) in a portion of her inner monologue (see book 7, Uncrowned). Yerin was relieved when he delayed his wedding to her, deciding first to go to Sacred Valley, because she was too emotional for stoic Yerin’s comfort.
He activated the Endless Sword. Every edged weapon in the room exploded with silver light. The Jade holding onto his wintersteel sword —— the weapon Min Shuei had gifted him before their parting —— fell to bloody chunks immediately and landed in a pile of gore. Adama caught the sheathed blade before it hit the ground. (Wintersteel, prologue)
From the flashback in Wintersteel's prologue: The Sage went into the Labyrinth in Sacred Valley, well-supplied with background information on Subject One, a researcher who became the first Dreadgod. He wanted to find out how to remove Yerin’s Blood Shadow without harming her spirit. He entered the labyrinth through the immense Ancestor’s Tomb, high on the slopes of Mount Samara, near Heaven’s Glory School. He’d been there for three months, the suppression field weakening his power daily until he was no stronger than a Jade. But he was weaker than he knew. Adama admitted to Yerin that he was willingly ingesting poison from Heaven's Glory school, who had provided housing for them, believing anything they could make would have no effect on a Sage. He was wrong.
Murder Scene: One night, a dozen elders of the Heaven's Glory school sneak up on Adama in his sleep. They all simultaneously stab him with poisoned half-silver blades. Adama fights back with as much power as he can muster in his weakened and poisoned body, eventually using his last strength to zap Yerin away to safety and to escape himself into the Ancestor's Tomb, where he succumbs to his wounds.
Thus it was that he died in the Ancestor's Tomb, an entrance to the labyrinth at Heaven's Glory School on Mount Samara. His power suppressed, he was slowly poisoned for three months, and once weakened, he was murdered by a dozen cowardly Jades with poisonous halfsilver blades, assisted by a bunch of Irons. His death occurred off-screen during book 1, Unsouled and is detailed in the Prologue of Wintersteel.
Halfsilver blades. Those would disrupt anyone’s madra, which explained the searing pain in his body and spirit, and halfsilver was unusually common here. Normally, they wouldn’t have penetrated his skin. He hadn’t considered the full implications of the strength being leeched from his Archlord body; it had been too long since any mundane attack was a threat. But. . .they had stabbed him. Though he was bleeding and surrounded by enemies, he still wondered if this could possibly be real. It was like a bunch of rabbits had taken up spears in their teeth and charged him. (Wintersteel prologue)
After he died, the murderers tried to take his Remnant. Yerin hated them and didn’t want them to defile her master’s last remains. Whilst Wei Shi Lindon, not even a Copper yet, successfully battled and killed a Jade, she battled the Remnant and won. Then the Remnant became her goldsign swords, brimming with sword aura. See Unsouled.
For over a year, Yerin tried to listen for her master within the Remnant. She expected it to still guide her on her Path. Finally she had to accept that her beloved master was truly gone. The Remnant was not the man. (See Blackflame, book 3)
More attacks landed, and he took another step. Another. His entire being fixed on the door, and his existence narrowed down to a singular purpose. He was going to that door, and these people would not stop Yerin from advancing. She would succeed him. Those were the two most prominent thoughts his Remnant inherited when it rose from his body. The door. And Yerin. (Wintersteel prologue)
His Void Space
The Sage stored copious notes about the Dreadgod dubbed Subject One in his void space, some of which came from Monarch Tiberian Arelius at House Arelius. About five years after he died, these notes were found by Wei Shi Lindon Arelius, thanks to Elder Whisper, who kept the void space open so it wouldn’t evaporate from non-use. Yerin reluctantly entered the void space and was tearful because he’d saved her old training robes (see Reaper).
Over the years, there has been much speculation surrounding his death, and fans constantly theorize about it on the Cradle subreddit (r/Iteration110Cradle), so much that it has become a fandom joke. Readers had to wait for the truth, until book 8, Wintersteel.