There are two distinct races of Straw Men.
The Straw Men were a race of golems created by the Iname, as part of their ultimate plan for vengence. What the Straw Men did not know, however, was that the Fall of Roads had happened and that the Eladamri no longer existed.
The Straw Men were created sometime during the Roads War, and laid down in various deep underground chambers (one such beneath the land of Rowen). Upon 'activation' the Straw Men would then begin one plan or another to wage war on the Eladamri.
Various uprisings are known throughout history, including a major one during Hunter's time. The Straw Men were also most likely responsible for the creation of eldritch SkyShips used throughout the Mage Wars.
The Straw Men are human-shaped though not always humanoid. They are made from a sort of semi-living clay, and are sentient, complete with free-will.