Gunnar Jauch wrote:

> Also the innocuous term "sleeper" got a whole new connotation.

    "Sleeper" has been around since after WWII (Cold War period) to describe
someone who lies-in-wait to create mayhem of some sort.  The OED's first
citation is

     1955 H. Roth Sleeper ix. 66 Hollister.. was a sleeper–a member of the
     Communist Party whose whole life was dedicated to the one big moment.

There was a great English tv film about two Russian sleepers who'd made lives in
England that they hated to give up.  Very funny and poignant.