Denis

Dennis (デニス, Russian: Деннис) 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.

Characteristics
Dennis 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. As a result of his past in the Soviet Union, he, like Simon, is a pacifist and tries to stop conflicts before they start.

Although his 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 Kyohei Kadota discuss rising tensions between the Yellow Scarves and the Dollars, Dennis 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 Dennis' 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
He 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. Dennis tells Niekawa Simon does not talk about fighting and sends him to talk to Izaya Orihara.

Yellow Scarves Arc
Dennis throws a knife into the room where Kyohei'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 Dennis tells them to not talk about gangs in the restaurant. Outside, Walker and Erika theorize that Dennis 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. Dennis, Simon, and Egor appear to be acquaintances and agree to help him. Dennis calls Shinra over to treat his wounds but he isn't able 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, Dennis, Simon, and Egor agree to help the Orihara twins meet Celty. He stuffs Egor into a bag and has Celty transport him for an entire day across the city. Dennis expects Celty to eventually reach her home where Egor will inform the twins of it's location. After the Toromaru members are taken care of, Egor tells Dennis and Simon of his desire to take a vacation from work.

Akane Arc
Dennis and Simon appear in Varona's flashback. They were apparently old friends of her father, Drakon, and agreed to teach her self defense. Varona 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 Varona and Sloan retreat to their hideout and then defeated by the Awakusu-Kai, Dennis, Simon, and Egor appear and reprimand the two of them for causing such chaos. Simon takes an unconscious Varona back to the restaurant while Sloan is taken by the Awakusu-Kai.