Shiryu

Shiryū was a Chief Jailer of Impel Down until he was imprisoned for his excessive violence towards the prisoners. During the riot caused by Monkey D. Luffy and Marshall D. Teach, he was temporarily freed to deal with the latter. However, instead of dealing with the pirate, Shiryū aided him and decided to join his crew.

Appearance
In a flashback, Shiryū was seen to have devil-like wings (these are absent when Shiryū made his actual appearance), like Magellan, along with an officer's hat that has ear-flaps on the sides, and maroon gloves. He usually has the bill of his hat rather low. He appears to be taller than an average man, as he towers over the regular guards. He also possesses a prominent chin. He was allowed to keep his uniform, rather than wearing the prisoners' striped shirt. He also wears a long jacket over it, draped over like a cape. The kanji on the back of his jacket reads Goku (獄), which means "prison".

Shiryū is usually seen smoking a cigar.

The sword that Shiryū wields is long (possibly a nodachi) and has a square guard. It has a white sheath, and dark in the middle portion.

Personality
Shiryū is extremely sadistic and seems to enjoy killing people any time he can. He massacred many prisoners within the walls of Impel Down, claiming them to be "trash". He also struck down his subordinates right after being released from prison, while giving a sarcastic apology. He also likes to test his blade against others, even if they are far below his level of power.

Shiryū is apparently very deceitful and treasonous, as he offered to help Magellan to fight for the prison if he is released, but instead betrayed his former superior and wreaked havoc and killed many subordinates.

Shiryū also believes that the Shichibukai are just pirates, as he refused to acknowledge Blackbeard as a "traitor", but rather just a "pirate". Despite this, he was easily willing to aid and join the Blackbeard Pirates. Like the Blackbeard Pirates' members, even before becoming one himself, Shiryū believes in fate. Having waited for someone like Blackbeard to come along, he believed that it was fate that brought Blackbeard to him, and that fate told him to join the crew.

Abilities and Powers
As former chief guard of Impel Down, Shiryū had command over lower ranking employees of the fortress. However, due to him abusing the power of his station, he was stripped of his rank and privileges.

His strength is also said to be comparable to the Chief Warden Magellan. However, since Magellan's work hours are limited by his diarrhea, Shiryū is considered more dangerous. Despite this, Magellan was still able to suppress Shiryū and place him in a cell in Level 6.

Apparently, Shiryū is a master swordsman and extremely proficient with a sword. As soon as he got released from his death row cell, Shiryū was given his sword back and killed his fellow Impel Down officers around in a split second. Shiryū also sees his sword as a living being, rather than an instrument of war, talking to it as a close friend similar to Roronoa Zoro.

Past
Though the guards of Impel Down have permission to kill prisoners for security reasons, Shiryū heavily abused that privilege by killing many prisoners for his own pleasure. When confronted by Magellan, Shiryū's abuse of his privilege was revealed and he was deemed to be a menace. For that, he was sentenced to death and put on death row in Level 6. As Level 6 prisoners' crimes are deemed too dangerous or embarrassing to be made public, Shiryū's crimes were not heard of by most prisoners, despite their brutality.

Impel Down arc
When the jailers reached Level 6, after their failed attempt to flood the floor with knock out gas to capture Monkey D. Luffy, Emporio Ivankov and Inazuma, Shiryū informs them that they had escaped, along with Jinbei and Crocodile, stating that Impel Down has gone downhill without him. He tells the jailers to pass word to Magellan that he would be willing to lend him a hand fighting against the escapees. Magellan, after hearing about Blackbeard's intrusion into Impel Down, reluctantly agreed to release Shiryū to fight against the unwelcome Shichibukai, adding that Shiryū's sentence has merely been postponed, and that he will not receive anymore chances. However, the moment he was given back his sword, he attacked the jailers who were sent to release him.

He is later seen at Level 1, confronting Blackbeard and his crew. What happened during their encounter is unknown, but the Blackbeard Pirates managed to bypass him and enter Level 4.

Later, Shiryū, seemingly unharmed from his encounter with Blackbeard, is seen slaughtering the guards, destroying the monitor room, disabling the giant Den Den Mushi that was responsible for visual reception, and severing all contact lines to the outside of the prison, while stating that he did not want Magellan to come down to where he is.

A while after the Blackbeard Pirates' encounter with Magellan, Shiryū came and saved them with an antidote, stating they would have died if it weren't for him. Blackbeard apparently invited Shiryū to join his crew before and repeated his offer after Shiryū saves them. Shiryū accepted, due to fate and the fact he was waiting for a man of Blackbeard's stature, and the alternative is being sentenced to death, as he stated himself. Shiryū is finally seen again when he came with Blackbeard to Marineford.

Marineford arc
Shiryū is spotted along with the other members of the Blackbeard Pirates on the execution platform where they were watching the events unfold on the battlefield. Currently, he and the others came to Marineford because they wanted to witness Whitebeard's death. When Sengoku demands to know what happened to Magellan and Impel Down, Shiryū replies by telling him to find out himself as he is now with Blackbeard. When Whitebeard manages to injure Blackbeard, despite the latter canceling out the Devil Fruit power of the former, Shiryū participates in attacking Whitebeard along with the rest of the Blackbeard Pirates, slashing him with his sword. After Whitebeard died, he and the rest of the crew proceeded to aid Teach in assimilating Whitebeard's Devil Fruit power by covering the two pirates in a dark blanket. Despite Teach emerging successful, Shiryū vocally states beforehand that there was a chance that Blackbeard could fail, musing whether or not the crew would go on or go about their separate ways if that happened. As Blackbeard takes control over the former powers of Whitebeard, he wants to shake Marineford to its core, making it sink. As Sengoku would not allow this to happen, he angrily transforms into his Buddha form. Then, creating a giant shockwave; he blasts away all the Blackbeard Pirates, except for the captain. As all of them fly away, he and Pizarro fly even further. It seems he doesn't have too much damage, as he was able stand up quite easily. He leaves with the rest of the crew when the Red Haired Pirates come on the scene.

Trivia

 * Shiryū shares his appearance with Yasunori Kato, the villain from the 80s novel and movie Teito Monogatari. Many other characters from anime and video games have been based on the same design, including M. Bison (known as Vega in Japan) from Street Fighter 2, and Washizaki from Riki-Oh. The design has been reused and referenced so often it is impossible to determine which character, if any, was the actual inspiration without confirmation from Oda himself.
 * Shiryū's name could be a reference to real life Chinese pirate Zheng Zhilong which, translated into Japanese, is Tei Shiryū. This however, remains unconfirmed by Oda.