Henry David Reginald Margesson, 1st Viscount Margesson PC (26 July 1890 – 24 December 1965) was a British Conservative politician most popularly remembered for his tenure as Government Chief Whip in the 1930s. His reputation was of a stern disciplinarian who was one of the harshest and most effective whips. This assessment has, however, been challenged by some, who argue from weaknesses of his system, and the number of high-profile rebellions during his tenure.