The Thorned Prince (real name Ren Takeru) first appeared in A New Fear Will Soon Be Born. His family was killed by The Slender Man, causing him to become a Runner. After some time, Slender Man ceased pursuing him, and Ren chose to settle down in a small town in Oregon. During that time, he became friends with a Willing Doll called the Samurai (aka Hiroshi Isamu).
After meeting Malkator, Slender Man began taking interest in Ren again, eventually sending a group of Proxies to bring him to the Path of Black Leaves. During this event, Ren was stabbed in the arm by a thorn from a Bleeding Tree. Shortly after, the Plague Doctor approached Ren and fused the thorn with Ren's arm.
Ren despises Slender Man, and has sworn to use his powers to destroy it.
He is often willing to put others in harm's way, if it will help him grow closer to killing Slender Man.
He is able to transform his arms into wood, and expand them indefinitely. Also, he has been known sprout leaves, bark, roots, vines, and thorns. He is a skilled swordsman.
His connection with the Bleeding Tree allows him to open portals into The Path of Black Leaves, and as a Servant to the Plague Doctor, he has access to The Crumbling Castle. He is able to grow stronger by drinking the blood of the Bleeding Trees, but it is heavily toxic.
Ren also displayed the ability to create Servants, which he calls "Saplings." He makes them by embedding seeds in peoples bodies, eventually giving him complete control over their bodies.