The twins are Mary and Kate Holsom respectively. They are pop stars that are often seen with Duke Nukem. They both have blonde hair, wear naughty schoolgirl outfits, and appear to be in their late teens. They are quite star-struck by Duke, making them especially eager to pleasure him with numerous sexual acts.
Both have similar personalities in that they have a quirky sense of humor, and enjoy making sexually suggestive jokes and puns. They often act very childish for their age, such as being deathly afraid of the dark every time the lights are turned off in a room, with each twin clamoring for Duke to comfort her over the other; both twins have also been shown giddily playing a game of tag in an almost innocent (albeit suggestive) fashion while waiting for Duke in the Lady Killer Casino.
Eventually they are captured by the aliens, and are taken to the hive to breed more aliens that will kill them. When Duke finds them in the Hive, they tell him of their plight, to which Duke can only respond: "Looks like you're... Fucked". They also exclaim that it was their first time (with an alien). Before he can find a way to comfort them from their despair, they give birth to baby Octabrains, exploding violently in the process. Duke vows vengeance on the Alien Queen and proceeds through the Hive.
- Their surname and the fact that they are twins are a reference to the Olsen twins. Their two first names are the same as Mary-Kate Olsen's first name.
- The twins appear to hold the rights to a toy franchise; a pink RC car, the Holsommobile, is named after them.
- Additionally, the Holsommobile contains a voice box that quotes lines from the Holsom twins themselves. These lines provide possible insight into more of the twins' personality and even their past, as it references their spoiled nature and how their mother had two boyfriends.
- Since they almost kiss each other in Duke's Casino (but are stopped by the aliens who abducted them), it is likely that they are incestuous.
- They are the main objectives for the game's Capture the Babe multiplayer mode.
- Despite being dead, they are available as unlockable babes in the My Digs mode, Duke will even ask of how they are alive.
- In the new Duke Nukem Forever: The Doctor Who Cloned Me (DLC), set immediately after the events of Duke Nukem Forever, the ever-rowdy Dylan makes a sexual reference to the now-deceased twins, but quickly apologizes to Duke after he realizes that their deaths still affected him.