quasi-proper name for a fox, c. 1300, Renard, from Old French Renart, Reynard, the name of the fox in Roman de Renart, from Old High German personal name Reginhart "strong in counsel," literally "counsel-brave." The first element is related to reckon, the second to hard.
The tales were enormously popular in medieval Western Europe; in them animals take the place of humans and each has a name: the lion is Noble, the cat Tibert, the bear Bruin, etc. The name of the fix thus became the word for "fox" in Old French (displacing golpil, gulpil, from a Vulgar Latin diminutive of Latin vulpes).
Old French also had renardie "craftiness." An old variant form of the name was Renald, and thus English had for a time renaldry "intrigue" (1610s). Old English had the first element of the name as regn-, an intensive prefix (as in regn-heard "very hard," regn-þeof "arch-thief," also in personal names).