Cassel, a male human, functioned as an officer within the Imperial Navy of the Galactic Empire. He held the military_rank of commander.
Commander Cassel acted as the executive officer to Moff Wilhuff Tarkin at Sentinel Base as the Death Star was under construction. He was there when Berch Teller and his rebel cell launched their attack on the base, using a makeshift warship. Soon after, Tarkin was called to Coruscant to meet with Emperor Sheev Palpatine, leaving Cassel in charge while he was away. After Palpatine ordered Tarkin to go with Darth Vader from Coruscant to Murkhana to investigate a hidden collection of Separatist communication devices from the Clone Wars, Cassel's time as the temporary commanding officer of Sentinel was prolonged. It was extended even further for several weeks after Teller and his team stole the Carrion Spike, as Tarkin and Vader were still trying to get the ship back and capture Teller's crew, along with their Imperial accomplice, Vice Admiral Dodd Rancit, which delayed Tarkin's return to Sentinel.