jack of all trades

(idiomatic) One competent in many endeavors, especially one who excels in none of them.

Example: 1618, Geffray Minshull, Essayes and characters of a prison and prisoners, p. 50:
  Now for the most part your porter is either some broken cittizen, who hath plaid Jack-of-all-trades, some pander, broker, or hangman, that hath plaid the knaue with all men, and for the more certainty his embleme is a red beard, to which facke hath made his nose cousin german.
1861, Charles Dickens, Great Expectations, ch. 25:
  "I am my own engineer, and my own carpenter, and my own plumber, and my own gardener, and my own Jack of all Trades," said Wemmick.
1912, Mary Roberts Rinehart, Where There's A Will, Ch. 5:
  A fellow can always get some sort of a job—I was coming up here to see if they needed an extra clerk or a waiter, or chauffeur, or anything that meant a roof and something to eat—but I suppose they don't need a jack-of-all-trades.