Douglas Harper's Etymology Dictionary
respelling of Old English hw- attested from 11c., but not the common form until after c.1400. It represents PIE *kw-; in German reduced to simple w-, in Scandinavian as hv-, kv-, or v-.\n
\nAlso added to some borrowed words ( whisk, whiskey) and some native words formerly spelled with simple w- or h- ( whole, whore). In the 15c. flowering of its use it also threatened to change the spelling of hot, home and many more. In northern English 16c.-18c., sometimes altered to quh- (see Q). Proper pronunciation has been much in dispute in educated speech.