He earned his nickname - Richard the Lionheart - during the Third Crusade. Initially accustomed to sieges, not battles, Richard surprised Saladin - conqueror of Jerusalem - when he decided to engage in actual warfare.
Throughout history, Richard I has been greatly honored and greatly vilified. John Gillingham provides reasons for this in "The Best of Kings, the Worst of Kings" (the first chapter in his biographical analysis, Richard I). Split into paragraphs, for easier reading:
Unique among the kings of England, Richard I played an active leading role in the great events of world history, in this case the struggle for control of the Middle East between two world religions, Islam and Christianity. By contrast, all other kings of England who ruled as well as reigned, no matter how clever, ambitious, able or power-hungry they may have been, confined their ruling and their campaigning to the north-western corner of Europe.
No earlier or later king took on a challenge remotely comparable with the task of taking a fleet and an army to the eastern end of the Mediterranean and there facing, even facing down, an adversary as formidable as the great Saladin.
Not surprisingly Richard I was for long seen as the greatest of English kings. According to Ranulf Higden, the fourteenth-century author of a world history which was both learned and popular, the Bretons boasted of their Arthur just as the Greeks of Alexander, the Romans of their Augustus, the English of Richard and the French of Charlemagne. Higden was not making a case for Richard, he was merely taking it for granted that this was how the English thought of him.
. . . In the last two or three hundred years orthodox opinion has judged Richard more harshly. 'He was certainly one of the worst rulers England has ever had.' That certainty was based on a consensus among the best and most influential historians which goes back at least as far as David Hume and Edward Gibbon.(Richard I, by John Gillingham, page 1.)
Clip of "Richard the Lionheart," from the BBC's series "Heroes and Villains." Online, courtesy BBC's Channel at YouTube. Copyright, BBC, all rights reserved. Clip provided here as fair use for educational purposes and to aquaint new viewers with the program.