Casido was a human lieutenant in the Imperial Navy of the Galactic Empire. In 1 BBY, they were stationed on the Imperial I-class Star Destroyer Intimidator and witnessed the arrival of a Rebel Alliance fleet above the planet Scarif from its bridge. Casido called for someone to get Admiral Gorin, but after the admiral arrived on the bridge the Intimidator was destroyed in the ensuing conflict.
Casido was a human officer in the Imperial Navy of the Galactic Empire. In 1 BBY, they held the rank of lieutenant and were stationed on board the Imperial I-class Star Destroyer Intimidator while it was part of the fleet that defended the Imperial Center of Military Research on the planet Scarif. When a Rebel Alliance fleet jumped into the Scarif system in order to support a group of rebels who had slipped passed the Imperials and made it to Scarif's surface to steal the plans to the Death Star superweapon, Casido was stood on the bridge of the Intimidator.
Witnessing the arrival of the fleet through the viewport, the lieutenant shouted orders for someone to fetch Admiral Gorin, Orbital Command of the Scarif fleet. Gorin then arrived on the bridge at some point during the ensuing conflict between the rebels and Imperials, which culminated in the destruction of the Intimidator when the disabled Star Destroyer Persecutor was forced to collide with it, allowing the rebels to successfully steal the plans.
Casido wore the uniform of an Imperial officer, including an Imperial kepi with an officer's disk and another disk on the buckle of their belt. The officer had a code cylinder on each breast and a rank insignia plaque with three blue pips and two red.
Casido was portrayed by Rufus Wright in the 2016 Anthology Series film, Rogue One: A Star Wars Story. The character's name is not spoken in the film but Wright's character is named as Lieutenant Casido in the credits. Wright filmed a large amount of dialogue as Casido, including lines about X-wing starfighters, but most of it was cut from the film's final release.
The scenes involved Gorin's actor, Michael Gould, and also included lines about the Intimidator being under repair and so unable to move. The scenes were blocked out by director Gareth Edwards before being filmed on a gimble on a sound stage set by the film's second unit. A chart of Imperial rank insignia created for Rogue One and released by costume designer Glyn Dillon lists the plaque worn by Casido as being that of a naval captain rather than a lieutenant.