Wordorigins.org

A Rube Goldberg device is an ingenious, overly complicated, and entirely impractical one. Reuben “Rube” Lucius Goldberg (1883-1970) was an American cartoonist famed for drawing cartoons of absurdly complicated machines for everyday tasks. Use of the term dates to at least 1938-39 when it appears in the Lexicon of Trade Jargon:

Rube Goldberg. Automatic machine; probably derived from this well known cartoonist’s humorous drawings of intricate but useless machinery.

This Lexicon also records plain Goldberg:

Goldberg. Cheap, complicated machine piece.

The earliest cite in the OED is in adjectival use, from The Amish Year (1956) by Charles Rice and Rollin Steinmetz:

The whole Rube Goldberg device is hitched to a wire which runs through ringbolts attached to short poles stuck in the ground, all the way to the house.

(Sources: www.doubletongued.org; Oxford English Dictionary, 2nd Edition)