The Decoy Queen is a alien queen and the main antagonist of Ben 10 Alien Swarm.
The Decoy Queen uses the body of Victor Validus as her host. Validus discovers he had been infected by the alien microchips called Nanochips and secretly starts studying other Nanochips found by the Plumbers. However he was caught removing them from the Vault and is accused of stealing them by Max Tennyson. Validus tries to warn Max about the Nanochips, but Max does not believe him and expels Victor from The Plumbers.
Validus keeps on studying the nanochips (which are actually collective members of the Hive), until he is completely taken over by the Queen. The Queen uses the Hive Chips to infect human hosts and plans to take over the entire planet Earth.
However her plan is thwarted by Elena Validus, Gwen Tennyson, Kevin Levin, and Ben Tennyson (in the form of his new alien, Nanomech). Even though she tries to control Nanomech, she is unable to do so as Nanomech is still half-human (because the chips can adapt and humans never give up, according to Ben, since that is what Ben said just before he killed her). She put up a brutal fight but in the end, the Queen is killed by Nanomech's bio-electric blast. With their Queen destroyed, the Hive quickly dies, freeing their victims and ending their threat.
In "Revenge of the Swarm", it was revealed Elena is the real queen of the Hive all along (the Queen in Alien Swarm was just a decoy produced so that Ben would not suspect her) in which she tried to keep Ben away from Julie Yamamoto in order to keep Ben all to herself. Ultimately, when she used the drones in an attempt to choke Ben to death, she was convinced by Julie to stop all this if she really loved Ben and at that moment Elena took control and sacrificed herself.