Random House Webster's Unabridged Dictionary, 1986 passim, shows first known usages for things insubstantial date to 1585-95. Universal Dictionary of the English Language, 1897, Vol 4, p. 4485, notes "man of straw" as "The figure of a man formed of an old suit of clothes stuffed with straw; hence, the mere resemblance of a man; one of no substance or means; an imaginary person."
Alternative forms 
- A doll or scarecrow (particularly one stuffed with straw).
- An insubstantial concept, idea, endeavor or argument, particularly one deliberately set up to be weakly supported, so that it can be easily knocked down; especially to impugn the strength of any related thing or idea.
- An innocuous person or someone of nominal or lesser importance, as a front man or straw boss.