Designed by Stuart Coffin circa 1975, made by Cubic Dissection 2002.
(6 pieces, bocote, 2.25 inches square assembled)

Here is what Coffin says in The Puzzling World of Polyhedral Dissections:

"The six-piece version of the 3 x 3 x 3 cube will be considered first. For aesthetic reasons, one might prefer that all the pieces be the same size, but this is impossible, so the nearest approximation is to use three four-block pieces and three five-block pieces. It is also desirable that all pieces be non-symmetrical but this is likewise impossible so two of the four-block pieces will have an axis of symmetry. All pieces will of course be dissimilar. Of the several thousand such combinations possible the author tried several that proved to have either multiple solutions or no solution, until finally finding one with a unique solution."

Here is the solution hint that was sold with the puzzle: