"Sir Forscale" is a miniature produced by Reaper Miniatures called Garrick the Bold (found here), sculpted by Bobby Jackson. He was used initially in the Reaper Bones Kickstarter as a miniature showing the scale of the more irregular miniatures, more humorously later in the Reaper Bones II Kickstarter with word bubbles and short blurbs interacting with the various miniatures. In Bones III he mostly took a backseat to Mr. and the newly introduced Mrs. Bones while still appearing for scale, and in Bones IV the Reaper team were forced to continually tell people requesting him to be added to the campaign that he's an already existing miniature that costs about a McDonalds cheeseburger on their website.
Despite the character Mr. Bones being the actual mascot for the Bones line, Sir Forscale (as in "for scale") has been popularized by fans and the otherwise unimpressive $1.99 miniature of a knight with shield and sword has seen a great deal of online posts of their own paintjob or him being slipped into a scenario ranging from space battles to medieval skirmishes to being the judge in a bizarre Paris Of Troy beauty contest between nightmarish lewd monsters. It's to the point that Reaper Miniatures' own website has it's own tag for "Sir Forscale".