Nothing is know of the history of the criminal known as Mister Laff prior to his appearance in Chicago in 1942.  It seems likely that he was already active and practicing his trade.  His first recorded case occurred when he mailed a cigar to a local tobacco store owner.  When the cigar was proffered, the owner took a puff, only to find it drugged.  Incapacitated, he sinks to the floor as the cash register is cleaned out.   Days later, a similar crime occurs at a liquor store where the owner if offered a gag whiskey bottle from which pops out a snake.  The owner takes it but the snake actually hides a poisoned needle, allowing another robbery.

Days later, Terry Sloane overhears the police commission describing the brazen string of prank-based crime.  When he shares the news with Wanda Wilson, she notes that a large stunt-themed charity ball is happening that night and Sloane deduces that it would be too good a target to resist.    That night at the ball, patrons are greeted by a room of floating balloons and offered slingshots to pop them provided by a mysterious donor.   As the guest start popping the balloons, they learn they are filled with noxious gas the incapacitates everyone in the room.  Mister Laff makes an appearance in a gas mask and begins collecting wallets and jewelry when Mr. Terrific rushes in.  Initially overwhelmed, Mister Laff gains an advantage when Wanda Wilson also rushes in and he managed to tangle her up with Mr. Terrific, abetting his escape.

Two days later, Wilson and Sloane here a radio broadcast about a convention of humorless people.  Realizing it would likely amuse Mister Laff to rob them, Sloane takes off as Mister Terrific.  Meanwhile, Mister Laff as dumped itching powder into the ventilation system, driving the conference attendees to distraction.  As he begin to rob them, Mr. Terrific appears and quickly takes the upper hand. Mister Laff beats a hasty retreat, reaching his car before Mr. Terrific leaps through an upper floor window and lands inside, capturing him for the police (Sensation Comics #12).

Any later activities of Mister Laff as well as his true identity have not been revealed.