Peter von Hagenbach (c. 1420 – May 9, 1474), also Pierre de Hagenbach, Pietro di Hagenbach, Pierre d'Archambaud, or Pierre d'Aquenbacq, was a Burgundian knight from Alsace, German military and civil commander, and convicted war criminal. The trial of Hagenbach was the first known trial of a war crime in history.

He was born into an Alsatian-Burgundian family, originally from Hagenbach, where they owned a castle.^{[citation needed]}

He was instated as bailiff of Upper Alsace by Charles the Bold, Duke of Burgundy, to administer the territories and rights on the Upper Rhine which had been mortgaged by Duke Sigmund of Further Austria for 50,000 florins in the Treaty of St. Omer in 1469. There he coined the term Landsknecht^{[citation needed]}—from German, Land ("land, country") + Knecht ("servant"). It was originally intended to indicate soldiers of the lowlands of the Holy Roman Empire as opposed to the Swiss mercenaries. As early as 1500 the misleading spelling Lanzknecht became common because of the phonetic and visual similarity between Land(e)s ("of the land/territory") and Lanze ("lance").

Following a rebellion by towns of the Upper Rhine against his tyranny, Hagenbach was put on trial for the atrocities committed during the occupation of Breisach. His trial, which was held by an ad hoc tribunal of the Holy Roman Empire in 1474, was the first "international" recognition of commanders' obligations to act lawfully.^[1][2] He was convicted of crimes, specifically murder, war rape, and perjury, among other crimes, that "he as a knight was deemed to have a duty to prevent". He defended himself by arguing that he was only following orders from the Duke of Burgundy, to whom the Holy Roman Empire had given Breisach.^[1][3] The ad hoc tribunal, however, refused to accept this as a defense. Peter von Hagenbach was found guilty of murder, rape, and perjury, and was beheaded at Breisach.^[4]

Although there was no explicit use of a doctrine of command responsibility, it is seen as the first trial based on that principle.^[4][5] It also includes the earliest documented prosecution of sexually-based/targeted crimes before an international tribunal when he was convicted for rapes committed by his troops.^[6] More recently, the trial of Peter von Hagenbach has been cited to argue against ongoing efforts in modern Australia seeking the retrial or posthumous pardon of convicted Boer War criminals Breaker Morant, Peter Handcock, George Witton, and Henry Picton.^[7]

• Burgundian Wars