etymology

Two very similar expressions yet quite opposite connotations. Wise man is an older phrase but wise guy is a newer one.

I found two possible connections to wise man. There is the surname Wiseman which is a long-established surname of Anglo-Saxon origin, and derives from the Olde English pre 7th Century "wys", meaning "wise", and "mann", a man, and was originally given as a nickname to a wise and learned man, perhaps one who was regularly consulted by other village inhabitants on matters pertaining to law or business transactions.1

Wise men is also mentioned as another name for biblical magi who were, in the Gospel of Matthew and Christian tradition, a group of distinguished foreigners who visited Jesus after his birth, bearing gifts of gold, frankincense and myrrh.2

Opposite connotations of the words from thefreedictionary:

wise man: a sage / a wise and trusted guide and advisor

wise guy: a smart aleck / a person who is given to making conceited, sardonic, or insolent comments

Etymonline says:

Wise man was in Old English. Wise guy is attested from 1896, American English...

1 http://www.surnamedb.com/Surname/Wiseman 2 http://en.wikipedia.org/wiki/Biblical_Magi