Slon

Slon (Russian: Слон) is a Russian assassin who was employed by a weapon dealing organization led by Lingerin Douglanikov and Drakon. He, along with Vorona, fled this organization with an entire truck full of stolen weapons and left for Japan.

Personality
Slon acts very relaxed and calm when not on a mission but gets rather talkative when he's actually working. Slon would often wonder about very trivial topics such as the nature of a cow's digestive system or why 13 is considered an unlucky number. It would even get to the point to where he states that he can't go on in life until he knows the answer, an answer which Vorona usually has. He speaks Japanese with broken grammar similar to how Simon does, however, with Slon it is done on purpose to throw his enemies off. He knows when to get serious and is very good at controlling a conversation when speaking with a client.

Appearance
Like Simon, Slon is extremely tall and has an overly muscular build. The novels describe him as looking very similar to a professional wrestler, and Vorona comments that he could lift an entire motorbike if he used both hands. He is also very adept at using firearms which makes him well-rounded as a mercenary.

Akane Arc
Slon and Vorona make their appearance near the beginning of the novel, witnessing Rokujo Chikage take down a robber. They enter a Karaoke bar where the meet their latest client, Yodogiri Jinnai. Slon drops his usual somewhat panicky persona and switches to that of a cold professional gun for hire. Yodogiri shows them a photo of Akane Awakusu and states that Slon and Vorona are to capture her. He also warns them about Celty who has been hired by the Awakusu to act as Akane's bodyguard.

Slon and Vorona accept the job and start investigating. After Vorona attacks Celty and returns to their hideout in a stolen delivery truck, Slon informs them of another job given to them by Izaya Orihara to injure, but not kill, Anri Sonohara. The two of them make their way to Anri's apartment and Slon waits in the truck while Vorona does her work. Slon notices Celty rushing towards them and warns Vorona that they should retreat.

After a brief chase which ends with Vorona blasting Celty away with an anti-tank rifle, the two mercenaries take refuge near a construction site. Slon and Vorona try to figure out how Celty managed to track them and notice a thin black shadow that is tied to Vorona's bike. They go to an abandoned warehouse and leave the bike near the back to lure Celty out into the open. Although Celty does indeed come, their plans are stalled by the arrival of Mikado, Aoba, and the remnants of the Blue Squares as witnesses.

Dollars and Blue Squares Arc
Vorona and Slon try to wait for them to leave but Celty ends up taking Mikado and riding away. Vorona opts to chase after Celty while Slon tries to find Akane. Much later, Vorona informs Slon that Akane and Celty are alone and that he should follow them. Slon catches up to Celty and waits for Akane to become vulnerable and sees his chance when Akane goes to hug her father, Mikiya. Slon throws a flashbang and grabs Akane as he drives by on his motorcycle. Celty gives chase but Slon manages to lose her long enough for him to switch to their get-away truck. Vorona contacts Slon that she is at Raira Academy and Slon drives over there immediately, unaware that Celty is following close behind.

Slon waits in the truck until Vorona comes in being chased by Shizuo. Vorona urges for Slon to drive, which he does, but they fail to shake off Shizuo and Celty. Eventually, Shizuo rescues Akane by destroying the storage compartment of their get-away truck and Slon and Vorona are forced to retreat. They head back to their hideout at the construction site where they discuss taking a vacation in Ikebukuro for a while. Their conversation is cut short by the arrival of Akabayashi and Aozaki, the Red and Blue Demons of the Awakusu, respectively. Slon and Vorona are easily incapacitated with Slon being taken in and forced to work for the Awakusu while Vorona is taken away by Simon.

At some point during volume 05, Slon was hired by Mikiya Awakusu to kill three spies within the Awakusu who worked for the police as well as rival organizations. This information was obtained by Izaya and used to frame Shizuo later on. Mikiya is seen fuming over how Slon betrayed him by kidnapping his daughter near the end of arc.

Adabashi Arc
Slon isn't seen until the end of the arc. where he is ordered by the Awakusu to keep tabs on Izaya by pretending to join forces with him. By this time, Slon has decided to conceal his identity by wrapping himself from head to toe in bandages and wearing a trench coat and hat.

Kadota's Coma Arc
At some point during the arc, Slon is attacked and defeated by a rogue child of Saika named Kujiragi who is allied with Yodogiri Jinnai. Under her influence, Slon is ordered to kidnap Izaya. He ambushes the information broker in his office and manages to knock him out.

Saving Izaya/Haruna is back Arc
Before Slon can leave, however, he is stopped by Mikage, Kine, and a few members of Zombie Dragon. A large fight ensues with Slon using Izaya as a club to take down most of the Zombie Dragon members. However, Mikage and Kine prove to be too much for him and he is forced to abandon his mission and escape.

Trivia

 * While spelled "Slon" on the Durarara!! official website, Слон, or "slon" in English, means "elephant" in Russian.