For Fernão Lopes the reign of Pedro I of Portugal and the Algarve (r. 1357–1367) was remarkable: ‘there had never been ten years in Portugal like the ones in which King Pedro … ruled’. Born in 1320, Pedro was the third but only surviving son of Afonso IV (r. 1325–1357) and his wife, Beatriz of Castile (1293–1359). As with many royal children, little is known about Pedro's upbringing and education. He was married in 1336 to Constanza Manuel of Castile who, not long before her death in 1345, bore him one son, the future Fernando I (r. 1367–1383). Pedro's early years, however, would be dominated by another woman and by his affair with one of Constanza's ladies-in-waiting, Inês de Castro. The remarkable story of their relationship, her murder perpetrated on King Afonso's orders, and the astounding brutality with which Pedro took his revenge on her killers, had major personal and political implications that would shape the king's reputation for the rest of his life and for posterity.

That reputation was and remains conflicted. The assiduousness with which the king sought out crimes, real or imagined, committed against himself or his nation was such that he became known to some as ‘the Just’ and to others as ‘the Cruel’. The latter appellation sometimes leads to confusion with his nephew, Pedro ‘the Cruel’ of Castile (r. 1350–1369), not least because the careers of the two men were closely entwined. This was, in part, because of the series of somewhat Byzantine dynastic crises and civil wars that bedevilled the Iberian Peninsula in the middle years of the 14th century. These struggles and the entangling alliances they involved encouraged the intervention of foreign powers, and it was during Pedro's reign that Spain and Portugal became deeply embroiled in the Hundred Years War (1337–1453), providing alternative theatres in which the Anglo-French conflict could be fought. Fernão Lopes recognised the wider European implications of these clashes, especially those that developed from the Castilian civil war fought between King Pedro and his half-brother, Enrique of Trastámara (King Enrique II, 1369–1379) and, because of this, he dedicated a considerable proportion of his chronicle to these events. Nineteen of the chronicle's 44 chapters concern Pedro of Castile.