Similar to Harley Quinn, Lock-Up was a character originally created in Batman: The Animated Series but had crossed over into comics. Surprisingly, Lock-Up was not character adapted into any of the Arkham games. However, his story would make for a great Most Wanted mission.
Lock-Up’s true identity is Lyle Bolton – a former Wayne Enterprises employee that specializes in security systems. Bolton was assigned by Bruce to Arkham Asylum in need of a new head of security. Unknown to Batman, Lyle Bolton stepped over the boundaries of the law by using excessive acts of torture and brutality to keep inmates in line. When fired at the discovery of his methods, he swore revenge on the corrupt system that creates a revolving door for criminals. He adopts the persona of Lock-Up to target reporters and government officials, but was thwarted by Batman. His incarceration ultimately did not trouble him as he was now able to keep a “closer eye” on his inmates.
As a potential mission, Lock-Up could have been a former GCPD cop / security systems expert at Arkham Asylum or Arkham City. Given the disastrous failures of these two institutions, and the outset of Scarecrow’s reign of terror, the Lock-Up persona was born. The mission could have Batman investigate mysterious disappearances or murders of GCPD cops, politicians, and reporters. This could ultimately come to its climax as a plot to lure out Batman, as Lock-Up believes it is his fault for making the city so unstable. Another interesting plot dynamic is if Lock-Up took over the GCPD headquarters with Batman having to lay siege to the compound and take it back.