Dimitri Kadmin, also known as Dimi the Twin is a hitman out of Vladivostok who worked a lot for the Yakuza. Since he trusted no one, Dimitri illegally copied his own Cortical Stack and placed it in another sleeve to create two versions of himself. Dimitri was hired to apprehend Takeshi Kovacs, but his sleeve and team were killed by Poe, the AI running The Raven Hotel where Kovacs had just signed in as a guest. Dimitri's Stack was intact enough to identify, but damaged enough to prevent spinning him back up for interrogation.
Dimitri hails from Vladivostok. At some point during his career, he copied his own stack and placed it in another sleeve, earning him the nickname "Dimi the Twin".
Throughout the series
Dimitri and some goons first appear at The Raven Hotel, demanding that Takeshi Kovacs come with them and beating him up when he refuses to cooperate. Takeshi instead checks into the hotel and fights off the thugs with help from Poe, killing Dimi's sleeve in the process and slagging his stack. Dimi's stack survives and is confiscated by Bay City Police, but it is too damaged for any form of interrogation.