What is the name of the detective created by Dorothy L. Sayers?

The detective created by Dorothy L. Sayers is Lord Peter Wimsey.

Wimsey first appeared in Whose Body? in 1923. He is an aristocratic amateur detective, eventually becoming the 17th Duke of Denver. His privileged background, sharp intellect, cultivated tastes, and playful manner make him a classic example of the British gentleman detective.

Sayers developed Wimsey across novels including Clouds of Witness, The Unpleasantness at the Bellona Club, and Murder Must Advertise. His investigations are often assisted by his valet, Mervyn Bunter, and his friend Charles Parker, a police detective. He later falls in love with crime novelist Harriet Vane, who becomes an important partner in both his personal life and investigations.

A common mix-up is confusing Wimsey with Agatha Christie's Hercule Poirot or Miss Marple, or with Raymond Chandler's Philip Marlowe. Those detectives were created by different authors and belong to different fictional traditions.