Denis

Denis (デニス, Denis, Russian: Денис) is an old friend of Simon Brezhnev and the owner of Russia Sushi. He works inside Russia Sushi as the chef, while Simon usually stands outside attracting customers.

Appearance
Denis is a large white man usually seen working behind the counter as a chef in Russia Sushi. As such, he is always seen wearing the Russia Sushi uniform.

Personality
As a result of his past in the Soviet Union, Denis, like Simon, is a pacifist and tries to stop conflicts before they start. He appears wise and well-connected, as he is able to offer sound advice and has the contact information of Izaya and Shiki. Unlike Simon, Denis speaks fluent Japanese, but he speaks up less than his partner.

Although Denis' strength is unknown, he is shown to have significant skill with knives, skills acquired both as a sushi chef and possibly from battle. When Masaomi Kida and Kyouhei Kadota discuss rising tensions between the Yellow Scarves and the Dollars, Denis throws his knife across their table to interrupt their conversation, alarming them all. As it is unlikely he actually tried to hit any of them, this indicates that he has very good aim.

Background
Not much is known about Denis' past other than he and Simon were former spec ops soldiers for the Soviet Union. Growing weary of a life of fighting, along with the collapse of the Soviet Union, he and Simon immigrated to Japan and opened a restaurant and have remained there for several years.

Dollars/Mika Harima Arc
Denis is shown working inside Russia Sushi whenever other characters come in to eat.

Saika Arc
Shuji Niekawa comes to Russia Sushi asking Simon who the toughest guy in Ikebukuro is. Denis tells Niekawa Simon does not talk about fighting and sends him to talk to Haruya Shiki.

Yellow Scarves Arc
Denis throws a knife into the room where Kyouhei's gang and Masaomi Kida are talking about the possibility of gang war. The knife cuts Saburo's hair before sticking into the wall, and Denis tells them to not talk about gangs in the restaurant. Outside, Walker and Erika theorize that Denis is a former Soviet agent.

Hollywood Arc
Mairu and Kururi stumble into the restaurant with an injured Egor, and they immediately bring him to the back. Denis, Simon, and Egor appear to be acquaintances and agree to help him while Egor tells them his reason for being in Tokyo. Denis calls Shinra over to treat his wounds, but he is unable to afford Shinra's fee of 200,000 yen. Mairu and Kururi offer to pay without a second thought.

In return for helping them with the bill, Denis, Simon, and Egor agree to help the Orihara twins meet Celty. He disguises himself and stuffs Egor into a bag, asking Celty to transport him for an entire day across the city. Denis expects Celty to eventually reach her home or another stopping point, where Egor will inform the twins of his location. Things do not go according to plan, and after the Toramaru gang members are taken care of, Egor tells Denis and Simon of his desire to take a vacation from work.

Akane Arc
Denis and Simon appear in Vorona's flashback. They were apparently old friends of her father, Drakon, and agreed to teach her self defense. Vorona excelled at the training and eventually expressed a desire to learn how to use weapons. They initially refused but eventually gave in to her demands. At some point afterward, they immigrated to Ikebukuro.

Dollars and Blue Squares Arc
After Vorona and Slon retreat to their hideout and then defeated by the Awakusu-Kai, Denis, Simon, and Egor appear and reprimand the two of them for causing such chaos. Simon takes an unconscious Vorona back to the restaurant while Slon is taken by the Awakusu-Kai.

Final Curtains Arc
He, Tom, Simon and Kine end up being trapped in Russian Sushi by the Saika Army.

Durarara SH
He overhears Yahiro and Kuon talk about Shizuo and tells them to stay away from him.