João das Regras, in English, literally John of the Rules, was a Portuguese jurist of the second half of the 14th-century. João das Regras was born in Lisbon in an unknown date and died there on 3 May 1404. Son of João Afonso das Regras and Sentil Esteves, João das Regras became a stepson of Álvaro Pais, the chief chancellor of the Portuguese Kingdom, after his mother's second marriage.
João das Regras became notable for supporting the claims of the grand-master of the Order of Aviz, João I to the throne of Portugal during the 1383–1385 Crisis, a period of civil war and anomie in the Portuguese history that began with the death of king Fernando I of Portugal — who left no male heirs — and ended with the accession to the throne of João I. During that period, several pretenders to the Portuguese throne arose and das Regras became notable for refuting the arguments of every one of them without mentioning the name of João I at the Cortes of Coimbra.
According to the Portuguese chronicler Fernão Lopes, João das Regras studied in the University of Bologna. Later, João das Regras became a professor in the University of Lisbon and in October 1400, became the Protector of the University (a title that nowadays can be compared to that of a Rector). His intervention in the Crisis began by influence of his stepfather, also a supporter of the grand-master, who had a major intervention in the Lisbon uprising, that would take João I to the throne. João das Regras was appointed by João I as his personal counsellor and supported the Master by pointing reasons that excluded the remaining pretenders to the throne, Beatrice of Portugal, Juan I of Castile, Denis, Lord of Cifuentes and John, Lord of Alba de Tormes, omitting the name of John I.