What is the name of the detective in 'The Mousetrap'?

The detective in Agatha Christie's The Mousetrap is Sergeant Trotter.

Trotter arrives at Monkswell Manor after a murder has been reported and the police warn that the killer may be connected to the guest house. He is introduced as Detective Sergeant Trotter, so “Sergeant Trotter” is the standard shortened answer.

The play is built around a confined group of suspects: the Ralstons, their guests, and a policeman investigating the crime. Trotter’s investigation gradually exposes links to a tragic incident involving three foster children, giving the mystery its central motive.

The other options are characters from different Christie stories. Superintendent Battle, Chief Inspector Craddock and Inspector Japp are recurring Christie detectives, but none is the investigator in The Mousetrap. A famous tradition also asks audiences not to reveal the solution after the performance.