Lieutenant Wion Dillems, a technological enthusiast from Yelsain, was a human male who sought unimaginable aerial speeds through technological advancement. As a pilot within the Alliance to Restore the Republic, he served aboard the Profundity, Admiral Raddus's mobile flagship. When pilot Puck Naeco suffered a broken ankle, Dillems took his place as Green Twelve within Green Squadron, stationed at the Great Temple on the moon Yavin 4. While on Yavin, Colonel Bandwin Cor included Dillems in a proposed flight operations plan.
By the time it was 0 BBY, Dillems was recognized as an ace, having successfully shot down or destroyed 180 enemy craft. He was present at a meeting within the Great Temple where the Alliance High Command decided against officially supporting a plan to acquire the plans for the Death Star superweapon from the planet Scarif. However, following an unsanctioned mission to Scarif by a group of rebel operatives, Dillems joined the Alliance Fleet that was dispatched to provide assistance. He and the rest of Green Squadron then engaged Imperial forces in the skies above Scarif.

Growing up among the Tree Dweller tribes in the vast forests of Yelsain, Wion Dillems was a human male who became a deadly hunter of Imperial craft after enlisting in the Starfighter Corps of the Alliance to Restore the Republic. By 0 BBY, he had earned the title of ace, with at least 180 enemy vessels destroyed or downed, and achieved the rank of lieutenant. Dillems was typically assigned to the Profundity, the flagship commanded by Admiral Raddus, which operated with the constantly moving Alliance Fleet. However, after pilot Puck Naeco sustained a ankle injury during a difficult landing, Dillems was called in as a last-minute replacement to fill the Green Twelve position in the Green Squadron of the Massassi Group, which was headquartered at the Great Temple on the moon of Yavin 4.
While Dillems was serving with Green Squadron, Colonel Bandwin Cor from Starfighter Command included him in a proposed flight schedule for patrol duties. This schedule involved flying a route between Yavin and the Gordian Trace Relays, visiting them in the order of coreward, spinward, and then rimward. The pilots were assigned to conduct flybys of the surrounding space, followed by a close uplink of passive relay recordings after confirming the area was clear. Dillems was assigned to shift cycle three, flying alongside Green Four, Lieutenant Attico Wred. General Jan Dodonna sent the proposed schedule to Mon Mothma, the leader of the Alliance, and it ultimately became part of the collection of documents known as The Rebel Files.

After rebel agent Jyn Erso brought news of the Empire's Death Star superweapon back to Yavin 4, a meeting took place in the Great Temple to determine the Alliance's response. Willems was present at the meeting, standing near Blue Leader Antoc Merrick as the Alliance High Command debated Erso's proposal to travel to the planet Scarif and steal the Death Star plans, which would expose a vulnerability in the Death Star that the Alliance could exploit. Ultimately, the plan failed to gain unanimous support, and the meeting concluded without a decision to proceed. Nevertheless, Erso led a rogue squad on an unauthorized mission to Scarif.
Upon learning about the events unfolding on Scarif, the Alliance Fleet was mobilized to provide support, including Dillems and the rest of Green Squadron. Upon the fleet's arrival in the Scarif system, Green Squadron engaged the Imperial forces in orbit, fighting alongside Red Squadron and Gold Squadron to defend the fleet. In the end, the Alliance successfully transmitted the plans from Scarif's surface and escaped, though they suffered significant losses. Fifteen fighters from Yavin 4 were destroyed, primarily from Red or Blue Squadrons.

Dillems wore an orange flight suit which had two code cylinders on its left sleeve, a white flak vest, and a Diagnostech life support unit. A black belt and flight gloves with a wrist-mounted comlink and beacon were also part of his gear. Dillems kept track of his personal tally of downed or destroyed enemy vehicles on his K-22995 light flight helmet, using a victory decal in a red or yellow circle for every twenty craft. By the time of the Battle of Scarif, there were at least nine decals on his helmet, which also featured a red and white chequered pattern above the visor, red markings down the back, and a black symbol on each side. The chequered pattern was similar to that worn by fellow rebel pilots Heff Tobber, Puck Naeco, and Wes Janson.
Dion Williams played Wion Dillems without credit in the film Rogue One: A Star Wars Story. Before the film's release on December 16, 2016, Dillems was featured on a card titled "Rebel Pilots" that was added to the Star Wars: Card Trader app on October 28, 2016.