Dukov

Dukov is a 43-year old drunken womanizing Russian with one of the foulest mouths in the Capital Wastes, and is one of the three surviving mercenaries hired by Allistair Tenpenny for an expedition into Fort Constantine. He is now retired to his estate (Dukov's Place) along the east bank of the Potomac in the D.C ruins. He spends his time drinking lots of alcohol and taking Jet with Cherry and Fantasia. He refers to the Lone Wanderer as "clown shoes" if the player is male and "sweet cheeks" if the player is female.

You Gotta Shoot 'Em in the Head
During the You Gotta Shoot 'Em in the Head quest in a dialogue with the Lone Wanderer, Dukov states he is no bigot as Mister Crowley claims and even had a Ghoul party girl once. To complete the quest you must obtain Dukov's Special Key from him. There are a variety of ways to do this.

Killing Dukov
If you inform him that you are "going to put a bullet in his head" he will rise to the challenge - the only difference is that you have VATS. Splatter his head at point blank and his party girls will not flee.

You can of course execute him outright, without provoking him, but his party girls will flee and not talk to you. Followers have a high risk of killing the innocent party girls and will result in a loss of karma.

Rather than just shooting him though, you can get a little creative and push him next to the motorcycle he has parked beside one of the two entrances on the bottom floor. Shoot the motorcycle until it explodes, avoid injury yourself, and the girls will not flee.

Non-violent solution
Talk with Cherry, she will pickpocket the key if you pass a speech check. In return she wants you to escort her to Rivet City for a karma bonus.

If you have the Lady Killer perk, you can convince Fantasia to acquire the key covertly from Dukov.

Alternatively, with the Black Widow perk, or by a difficult Speech check, you can convince him to just give you the key.

Also, with the use of a Stealth Boy or moderate sneak skill, you can simply pickpocket Dukov's special key off him. Successfully pickpocketing him will not turn him, Cherry, or Fantasia hostile. If you fail, they will turn hostile, causing Dukov to attack and the girls to flee.

Bugs

 * There is a glitch that occurs after you kill Dukov. If you wait two weeks and return to loot his house, a Deathclaw will enter the room after you have stolen a few items.  This only occurs once.  If you die, it will not occur again.
 * Even though Dukov always talks about drinks - and that you should serve yourself - if you steal more than two bottles he will become hostile and attack you. The girls will be marked hostile as well. However, this can be avoided if you take drinks from the cabinet in the bedroom upstairs.
 * Occasionally if Dukov dies he can still be heard talking through his normal dialogue with the girls. (PS3 Version)
 * There is a glitch where Dukov's special key cannot be used with Fort Constantine.
 * There is also a glitch where the Black Widow perk will not affect Dukov.
 * Occasionally, after you kill Dukov (if you decide to outright kill him), the girls will flee upstairs into their sleeping quarters and inexplicably die. You can find them lying on the floor, dead, sometimes with one's head severed from the rest of the body. (Unconfirmed for 360 and PS3 versions)

Appearances
Dukov appears only in Fallout 3.

Behind the scenes
Going by a cut note found in Fallout 3's game files Dukov either used to be called "Vando" earlier in development or replaced said Vando.