Choyyssyk was a Wookiee male commander who served within Chieftain Tarfful's resistance group on Kashyyyk during the Imperial Era; Wookiees are from the planet Kashyyyk. This Wookiee was captured and then imprisoned inside the Imperial Refinery, but he was later freed thanks to the efforts of both Saw Gerrera's Partisans and the former Jedi Padawan, Cal Kestis. Following his liberation, Choyyssyk collaborated with the Partisans and developed a friendship with Mari Kosan, who served as Gerrera's lieutenant. When most of the Partisans departed from Kashyyyk and Kestis made his return to meet with Tarfful, Choyyssyk, along with Mirienna, was present at Cargo Pad 119-Grek.
During the Galactic Empire's occupation of Kashyyyk, his species' homeworld, Choyyssyk, a Wookiee, resided there. He held the rank of commander within the Kashyyyk resistance, which was under the leadership of Chieftain Tarfful. However, he was taken prisoner during a mission to attack an Imperial outpost and subsequently imprisoned in an Imperial Refinery. At the refinery, enslaved Wookiees were exploited for the harvesting of Wroshyr sap. Forced to wear a slave collar, Choyyssyk remained in the refinery for several months because Tarfful considered it too risky to send any warriors to attempt a rescue.
In 14 BBY, the fugitive Jedi Cal Kestis entered the cell block where Choyyssyk and many other Wookiees were confined. Choyyssyk called out to Kestis as the Jedi tried to unlock the cells. The Jedi assured the prisoner that he was going to be freed, but before Kestis could open the cell doors, a KX-series security droid launched an attack from behind. After the Jedi defeated the droid, he opened the cell doors, prompting cheers from Choyyssyk and the other Wookiees as they escaped. Choyyssyk even embraced Kestis.
The Wookiees then joined forces with Saw Gerrera, an ally of Kestis, and his Partisans as they fought their way through the facility, eventually reaching the roof. Once there, with the Imperial forces defeated, Gerrera delivered a speech to those present. Following this, Choyyssyk and the Partisan Mari Kosan approached Kestis, who inquired whether Choyyssyk knew Tarfful. With Kosan translating Choyyssyk's Shyriiwook for Kestis, the Wookiee pledged to do everything possible to locate Tarfful for Kestis, while also explaining that it might take some time since Tarfful was constantly on the move. Kestis expressed his gratitude before departing from Kashyyyk, confident that Choyyssyk and Kosan would succeed in finding Tarfful for him.
After his liberation from the refinery, Choyyssyk utilized a DC-15A blaster carbine.
Choyyssyk made an appearance in the 2019 video game Star Wars Jedi: Fallen Order, developed by Respawn Entertainment.