|“||So scared you locked me away, huh? Think you can can get rid of me this easy!?||„|
|~ Leo Kasper|
Leo was a former assassin that worked for the government. He was trained by the Project in skills such as assassination, combat, infiltration, and evasion. Leo first appeared guiding Danny in escaping from an asylum, and guided him into becoming a killer.
Even though he helps Danny, the latter is almost always did all the work. Later, in the level Origins, Leo interrogates Dr. Pickman, their captive, into removing the Pickman Bridge. The latter tells the former that doing that is a bad idea since it will kill him.
When Danny is captured, Dr. Whyte reveals more of Leo. It turns out that Danny worked as a scientist in implanting a second personality into an individual. This personality would be a killer with no conscience or memory. It is Leo, and Whyte says that they're two minds in one body unaware of each other. Unfortunately, the Bridge malfunctioned, explaining of how Danny and Leo talked all the time.
Even so, Danny refuses to get rid of Leo because he saved his life. Whyte shows him his profile to see that his house is burned down under Pickman's orders. Luckily, his kids are fine, but when Danny asks about his wife, Whyte hesitates at that. Instead, she shows him a video tape to help him understand why he must let go of Leo. It is revealed that he killed Mrs. Lamb when he took control of Danny, causing Danny himself to go in a trance to release Leo.
In Personality Clash, Danny kills Leo in the cemetery setting in his mind. This not only leads to having a free mind, but also in losing his memories.
In Release Therapy, Leo has won in the battle with Danny in the library setting in his mind. He kills him, leading him to take over Danny's body. When he woke up, he ordered Dr. Whyte to get a scientist team to remove the Pickman Bridge. Danny washes his face, and in the reflection shows Leo, a sign that he dominates his body and mind.