Casido was a lieutenant serving the Imperial Navy, a branch of the armed forces of the Galactic Empire; they were a human. During the events of 1 BBY, they were stationed on the bridge of the Intimidator, an Imperial I-class Star Destroyer, and from that vantage point, they observed the arrival of a Rebel Alliance fleet above the planet Scarif. Casido then gave orders for someone to summon Admiral Gorin to the bridge. However, following the admiral's arrival, the Intimidator met its end amidst the unfolding battle.
Casido was a human officer within the Imperial Navy, serving the Galactic Empire. In 1 BBY, holding the rank of lieutenant, they were assigned to the Imperial I-class Star Destroyer Intimidator. At this time, the Intimidator was a part of the fleet tasked with defending the Imperial Center of Military Research located on the planet Scarif. Casido was present on the bridge of the Intimidator when a Rebel Alliance fleet entered the Scarif system. The Rebel fleet's arrival was in support of a group of rebels who had managed to evade Imperial forces and land on Scarif's surface with the objective to steal the plans for the Death Star superweapon.
As the fleet came into view through the viewport, the lieutenant issued an order for someone to summon Admiral Gorin, who was in charge of Orbital Command for the Scarif fleet. During the battle that followed between the Rebel and Imperial forces, Gorin made his way to the bridge. The conflict ultimately led to the destruction of the Intimidator when the crippled Star Destroyer Persecutor was deliberately crashed into it, which inadvertently aided the rebels in their mission to successfully retrieve the plans.
Casido was clad in the standard uniform issued to Imperial officers, complete with an Imperial kepi adorned with an officer's disk, and another disk affixed to the buckle of their belt. The officer also carried a code cylinder on each breast and bore a rank insignia plaque displaying three blue pips and two red ones.
Rufus Wright played Casido in Rogue One: A Star Wars Story, a film released in 2016 as part of the Anthology Series. While the character's name is not spoken in the film itself, the credits identify Wright's character as Lieutenant Casido. Wright recorded a substantial amount of dialogue as Casido, including lines pertaining to X-wing starfighters, but much of this material was ultimately removed from the final cut of the film.
The scenes, also featuring Michael Gould as Gorin, contained dialogue indicating that the Intimidator was undergoing repairs and therefore unable to maneuver. Director Gareth Edwards mapped out the blocking for these scenes before they were shot on a sound stage set mounted on a gimbal by the film's second unit. A chart displaying Imperial rank insignia created for Rogue One and shared by costume designer Glyn Dillon identifies the plaque worn by Casido as belonging to a naval captain, rather than a lieutenant.