Commander Cassel served as Moff Wilhuff Tarkin's executive officer at Sentinel Base during the construction of the Death Star. He was present during the attack against the installation by a cobbled-together warship commanded by Berch Teller and his rebel cell. When Tarkin was summoned to Coruscant to meet with Emperor Sheev Palpatine shortly thereafter, he left Cassel in command during his absence. Cassel's tenure as temporary commanding officer of Sentinel while Tarkin was gone ended up being extended following Palpatine's command that Tarkin accompany Darth Vader from Coruscant to Murkhana to investigate a cache of Separatist communications devices left over from the Clone Wars, and then for several weeks longer following the theft of the Carrion Spike by Teller and his crew, as Tarkin's return to Sentinel continued to be delayed by his and Vader's efforts to recover the ship and capture Teller's crew and their Imperial co-conspirator Vice Admiral Dodd Rancit.
- Tarkin (First appearance)