Who serves as the Slap Bet commissioner?

Lily serves as the Slap Bet commissioner in How I Met Your Mother.

The role is established during the original bet over why Robin refuses to go to malls. Marshall believes Robin secretly married in Canada, while Barney suspects a more scandalous explanation. Instead of wagering money, they agree that the winner will be allowed to slap the loser, and Lily is appointed to enforce the rules.

As commissioner, Lily decides when slaps are permitted and imposes penalties for violations. After Marshall prematurely slaps Barney and Barney later slaps Marshall without authorization, Lily rules on the consequences. She gives Barney a choice between receiving ten slaps immediately or allowing five slaps to be delivered at any time.

Lily's authority continues throughout the storyline. She can suspend slaps, as she does during Thanksgiving, and later approves additional terms connected to Barney's duckie tie. Marshall delivers the physical slaps, but Lily remains the official commissioner who interprets and administers the bet.