|Business:||Accountant of Vera Montello|
|Family:||Unnamed deceased father|
|Allies:|| Jason Malone|
Benny (later on)
|Enemies:|| Frank Veliano|
Karen Olsen is a major character appearing in Gangstar Vegas.
At some point, Karen tells Jason about her past. Her mother ran away with an Elvis Presley look-a-like and she was raised by her father, who was a policeman working against the Mafia. Eventually, her father was killed in an alleyway later on. His murderer later turns out to be Frank Veliano, the game's main antagonist.
Events of Gangstar Vegas
Karen makes her first appearance when Jason's car is rammed by a Veliano mob vehicle shortly after his fight against Pietro Holston. Frank's henchman gets out of his vehicle and wants to execute Jason, but in the same moment is run over by Karen's red D340. She introduces herself as the accountant of Vera Montello, whom Jason had called during the chase. Karen helps him get out of the car and they escape the rest of the henchmen.
After this, Jason and Karen do some jobs against Veliano together, like attacking his construction site. However, at some point, Frank, Benny and some gangsters attack Vera's strip club, where she is hanging out with Karen and Jason. Karen is hit by a bullet during the shootout. She and Vera are covered by Jason in order to leave the club, while Jason himself is captured by Veliano and forced into working for him.
Karen and Jason keep in touch on the phone. After some time has passed, Jason and Benny burn down a trailer park where some members of the hispanic Huevos are hanging out. Benny talks about a package that they have to retrieve. While Jason takes down the Huevos, Benny gets the "package" in the trunk of Jason's car. After they've met up again, they drive to the spot where they're supposed to meet Frank. During the ride, Jason notices that the "package" is a human, and it turns out to be Karen after they have met with Frank. Frank had Karen kidnapped in order to blackmail Vera Montello into delivering herself to him so that he could kill her and take over her territory.
With the help of E-Man, Jason manages to detect Karen's position. They find out that she's being held at Frank's casino and so Jason, Vera and E-Man break into the casino in order to free Karen. They find her on the helipad being held by Benny, who threatens to kill her. Eventually, they manage to free Karen. To make Benny look like a hero, Jason beats him up so that Frank doesn't kill him.
After Vera's suicide and the other three's escape, Karen tells Jason that Frank has confessed that he was the one behind Mr. Olsen's death (Karen's father). The fact that he is proud of it makes Karen keen on killing Veliano. They take Vera's strip club back and do some other jobs against Veliano, during one of which Karen is eventually heard kissing Jason in his car before they drive off. At some point, they rescue Benny, who has been arrested and is to be killed by the Veliano mobsters, from Frank's henchmen and thereby bring him over on their side. After causing chaos at Veliano's place and leading the press to this case, Karen, along with E-Man and Benny, helps Jason turn Goodman against Veliano.
Thereafter, Karen and Benny help Jason get to the helicopter and fly over to Frank's location. After Jason has defeated Frank, he parachutes into Karen's bypassing Störer and they drive off.
- After she and Jason have taken back the strip club from Veliano, she takes over the owership of the place and runs the business there. In the radio, it is said that there have been shooting noises, but Karen claims that these noises come from the renovation process going on in the strip club
- As already mentioned, Karen and Jason kiss at some point. Vera had already seen that Jason had "moon eyes" for Karen (which means that he likes her), so this suggests that Karen has fallen in love with Jason. However, it is unknown if they start a relationship after that.