Shiryu

Shiryuu 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, Shiryuu aided him and decided to join his crew.

Appearance
In a flashback, Shiryuu was seen to have devil-like wings (these are absent when Shiryuu made his actual appearance), like Magellan, along with an officer's hat that has ear-flaps on the sides, and black gloves. He appears to be taller than an average man, as he towers over the regular guards. 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".

Shiryuu is usually seen smoking a cigar.

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

Personality
Shiryuu 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.

Shiryuu 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.

Shiryuu 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, Shiryuu 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, Shiryuu had command over lower ranking employees of the fortress. However, due to his abuse of powers, 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, Shiryuu is considered more dangerous. Despite this, Magellan was still able to suppress Shiryuu and place him in a cell in Level 6.

Apparently Shiryuu is a master swordsman and extremely proficient with a sword, as soon as he got released from his death row cell, Shiryuu has given his sword back and slayed the fellow marine officers around in a split second.Shiryuu also sees his sword as a living being rather than an instrument of war, talking to it as a close friend similar to Ronoroa Zoro.

Past
Though the guards of Impel Down have permission to kill prisoners for security reasons, Shiryuu heavily abused that privilege by killing many prisoners for his own pleasure. When confronted by Magellan, Shiryuu'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, Shiryuu'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, Shiryuu 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 Shiryuu to fight against the unwelcome Shichibukai, adding that Shiryuu'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, Shiryuu, seemingly unharmed from his encounter with Blackbeard, is seen slaughtering the guards, destroying the monitor room, disabling the giant Surveillance 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, Shiryuu came and saved them with an antidote, stating they would have died if it weren't for him. Blackbeard apparently invited Shiryuu to join his crew before and repeated his offer after Shiryuu saves them. Shiryuu 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.

Trivia

 * His appearance appears to be based off of 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 from Street Fighter 2, and Washizaki from Riki-Oh.
 * He and Lafitte are both former World Government affiliates who were stripped of their positions and punished for abuse of privileges (murderous Impel Down Chief Guard given death sentence and excessively violent policeman exiled, respectively).