“I'll turn your mustache into a bone-polisher, amigo!”
Cortez is the holder of the fifth Crystal Star, the Sapphire Star, in Paper Mario: The Thousand-Year Door. During dialogues, he appropriately speaks in a Spanish accent. He resides on a pirate-ship-like vessel, deep within Pirate's Grotto on Keelhaul Key. He tries to scare Mario away (like what Tutankoopa did in the first game) when he thinks the plumber is after his treasure; when his eerie messages fail, he drops the act in disgust and begins a battle.
After being defeated, Cortez seemingly prepares to vanish, only to reveal that his state of unlife renders him effectively invincible. However, Mario is finally able to explain that he wasn't interested in Cortez's treasure, only in the Crystal Star. Somewhat bemused and wondering why Mario "didn't just say so" in the first place, Cortez willingly hands over the artifact, offhandedly remarking that he never particularly cared for the Crystal Star anyways.
After Four-Eyes revealed his true identity as Lord Crump, Mario and Flavio return to Cortez, in order to request the use of his ship. Cortez was not particularly interested, spouting that he didn't want his ship to be used as a luxury liner. He also tells them that even if he wanted to lend them his ship, the ship is useless, as it won't operate, because of the loss of its power source, the Skull Gem. Flavio then reveals he has the gem, causing Cortez to be even more furious, and not wishing to help them even further, as Flavio's ancestors stole it from him. He eventually relents after Flavio reminded him that Mario defeated him once, and hints he'll have Mario fight Cortez again for the ship. He also says that if Cortez doesn't help, he'll throw the Skull Gem into the water where Cortez will never find it. After hearing this, Cortez, relenting, then helps them in the battle against the X-Nauts when Lord Crump attacks Keelhaul Key. From then on, Cortez stays docked at Rogueport, and would ferry Mario to Keelhaul Key and back whenever he wanted. In this regard, he serves much the same purpose as The Whale from the first Paper Mario.
In battle, Cortez has three forms. His first form appears as a massive skeleton with four arms and no legs, with his spine emerging from a spiky pile of bones on the ground. His limbs all terminate in various weapons - a large sword, a curved sabre, a thin rapier, and a rusty hook that can cause poison- enabling him to attack either or both heroes every turn. If this form is defeated, Cortez transforms into a serpentine state, trading the arms and weapons for an enlarged rib cage concealing a green gem. This form attacks with a headbutt, and can charge before throwing a bone at either character, dealing great damage in the process.
After his second form is defeated, Cortez reverts to his "natural" state, a mere floating head. Although he is limited to a simple bite attack, he compensates by animating his discarded weapons, effectively giving Mario and his partner five opponents to worry about. The weapons have different properties to their attacks, and are immune to frontal attacks due to their pointed tips; however, they can be destroyed simultaneously by a moderately strong attack that hits all opponents. If Cortez takes heavy damage, he can also absorb the souls of the Audience to restore his HP, similar to Hooktail and the Shadow Queen. The only difference is that Cortez can only absorb souls equal to half the current audience members while the Shadow Queen will absorb them all and Hooktail scares away the uneaten members. However, it is possible to defeat Cortez before he gets a chance to absorb the audience.
Cortez is the one who defeated the Stalwart Koopa and caused him to be sealed in a magic Black Chest.
Names in other languages