Words of Radiance, |
Arcanum Unbounded (unnamed, mentioned),
Edgedancer (unnamed, mentioned)
Ym was a cobbler who made shoes in the old way. He'd observed that a "sparkling light spren" made increasingly frequent visits to his shop and that it was a kind of spren he'd not seen before. Ym spoke to the spren while working and it responded: "He comes." 
While Ym treated a cut on the foot of a young street urchin, he held a broam in his hand, the light from which vanished as he healed the cut and removed the infection. He knew the spren was involved in what he did. For the shoes he made for the urchin, Ym asked for his story.
After the urchin left, the spren warned him: "He's still here ... ." A man with dark, Makabaki skin emerged from the shadows and confronted Ym with his past. After a brief chase, the man killed Ym with a Shardblade shoved through his chest.
Ym was previously a "carouser" ...
|“||"A young man of means who drank and partied away what his parents left him." ||”|
He was also a murderer ... or an accomplice to the murder of a woman, the poison delivered in a bottle of wine that he gave her. He'd been desperate for money and the vintage was supposed to indicate to her that she needed to pay those from whom Ym received the bottle. He claimed he didn't know it would kill her.
Ym believed that all beings were One; that all beings were separate minds of a single being experiencing different lives.
|“||"Long ago, there was only One. One knew everything, but had experienced nothing. And so, One became many - us, people. The One, who is both male and female, did so to experience all things." ||”|
However, he accepted no god. Neither did he accept priests as they were from other lands. He believed that all Iriali were part of the Long Trail, of which the ground upon which he stood was the Fourth Land. Further, he believed that the Iriali people needed no preaching, only experience.
|“||"As each experience is different, it brings completeness. Eventually, all will be gathered back in - when the Seventh Land is attained - and we will once again become One." ||”|
Additionally, he believes that as One, the people know truth; as many, they need ignorance.
|“||"We exist in variety to to experience all kinds of thought. That means some of us must know and others must not - just like some must be rich, and others must be poor." ||”|
Even so, he believes that all peoples will ultimately arrive in the same place.
|“||As much time as I spent with Team Sanderson last weekend, we spent oddly little time talking about the books. One question I did ask Brandon, though, was whether Ym was an Edgedancer. We both acknowledged that with the healing thing, he had to be either an Edgedancer or a Truthwatcher, of course. He pointed out that Ym’s spren doesn’t look at all like Wyndle, which I countered by saying that I thought [that] Ym’s spren manifested the way Wyndle would if you couldn’t see the Cognitive Realm. He just smiled ... and said something like, "I’m going to RAFO that. You’re very wise, and I put the description in for a reason, but I’m going to RAFO for now."||”|
Without naming him, Wyndle brings up Ym in conversation with Lift and comments that what a nice co-existence he could've had with the cobbler. That Ym was a very kindly man who took care of children. That he could have lived quietly, helping Ym, making shoes.
|“||"I could have done an entire display of shoes!||”|
–Wyndle to Lift