A dictionary of Proverbs (Oxford Paperback Reference)

JACK is as good as his master
Jack is variously used as a familiar name for a sailor, a member of the common people, a serving man, and one who does odd jobs.

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  1706 J. STEVENS Spanish & English Diet. s.v. Pedro, Peter is as good as his Master. Like Master, like Man. 1868 READE & BOUCICAULT Foul Play II. xx. Is it the general opinion of seamen before the mast? Come, tell us. Jack’s as good as his master in these matters. 1936 W. HOLTBY South RidingI. iv. She was far from thinking Jack as good as his master and explained failure in plebeian upstarts by saying with suave contempt: ‘Well, what can you expect? Wasn’t bred to power.’ 1987 R. HILL Child’s Play viii. 1945 might have seen Britain ready at last for the political assertion that Jack was as good as his master, but it was still light years away from any meaningful acknowledgement that Black Jack was as good as White Jack. ■ employers and employees; equality
  

JACK of all trades and master of none
Jaek is used here in the sense of unskilled worker, as contrasted with a master of a trade who had completed an apprenticeship.

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  1732 T. FULLER Gnomologia no. 3051 Jack of all Trades is of no Trade. 1804 M. EDGEWORTH ‘The Will’ in Popular Tales ii. 152 ‘How comes it that I am so unlucky?’ ‘Jack of all trades, and master of none!’ said Goodenough, with a sneer. 1878 S.
  

WALPOLE History of England I. 311 It would be unfair to say of Lord Brougham that he was ‘Jack of all trades and master of none’. 1987 O. S. CARD Seventh Son (1988) vi. 47 To have every possible skill.. and to have it in exactly even proportions. Far from being average, the child was extraordinary..Jack of all trades and master of none? Or master of all? 2002 Oxford Times Weekend 9 He is quick to point out that the reverse side of the renaissance man is jack of all trades, who, as we all know, is often considered a master of none. "trades and skills