Jaylen Kos was a youngling of the Iridonian Zabrak species. He was located at the Jedi Temple on Coruscant throughout the Clone Wars. The Padawan of Bant Eerin was his closest friend. When the aforementioned pilot was en route to assist his master within the Kashyyyk system, Kos secretly boarded his friend's Jedi starfighter. This headstrong young Jedi in training felt bitterness because Ahsoka Tano had been assigned to a Jedi Knight as a Padawan before he himself had.
Kos's only appearance was in The Clone Wars: Decide Your Destiny: The Way of the Jedi. He was the best friend of the book's main character, who was designed to represent the reader. The reader's choices concerning Bant Eerin's Padawan's actions directly determined Kos's destiny, with as many as 26 different possible outcomes, both positive and negative.
Within a galaxy of endless possibilities, Kos's destiny was profoundly shaped by the choices of his young Jedi apprentice friend. He could become a hero alongside his friend, earning his own Jedi Master for training, or succumb to the dark side of the Force and aid Asajj Ventress.