Marcus Davenport

Marcus Davenport is the overall secondary antagonist of the 2012-2016 television series Lab Rats. He is an Android created by Douglas Davenport (who he considers his father) and the Android brother of Adam, Bree, Chase, and Daniel and step-cousin of Leo Dooley and the nephew of Tasha Davenport and Donald Davenport. Marcus has all four of the Lab Rats' powers and abilities: Adam's super strength, Bree's superspeed, Chase's superintelligence and later, Leo's laser sphere generation.

The Lab Rats
The Lab Rats consists of Marcus's adoptive cousins, Adam, Bree, Chase, and Leo. While Adam, Breeand Chase were convinced that Marcus was their friend, and a kind and trouble boy, Leo was the only one to know of Marcus's true colors: conniving, cold-hearted,a murderous. Marcus threatened to reveal their bionic secret if Leo ever reveals that Marcus was bionic and after them. However, Adam, Bree and Chase never believed their younger brother until the events of Bionic Showdown. After it was revealed that Douglas, Marcus' creator, this made Marcus Adam, Bree and Chase's Android brother and adoptive cousin and Leo's step-cousin. After Marcus supposedly killed Leo, Adam, Bree and Chase came to hate him and wanted to avenge their little brother's death. During their confrontation after the kids and Donald escaped, Chase called Marcus a "creep" and Adam later attacked Marcus with his new bionic ability in order to protect Leo. The kids were shocked when Marcus was recreated in the year 2016.

Trivia

 * Marcus and Daniel are the only ones who called Douglas "Dad" as their siblings, Adam, Bree and Chase call Douglas their uncle.

Suddenly Bionic
In Suddenly Bionic, when Donald scolds Douglas, he tells him to train Leo and look after him, mentioning to be careful because the last person he trained with Bionics had tried to kill them.