Sentence:  What was required now was the intervention of some men who were not <WSD>gadflies</WSD>. [...] The logic of Pearson's arguments was accepted, up to a point, by a consortium of businessmen. In August 1854 [...] the consortium  obtained royal assent for [...] the Metropolitan Railway. [...] In 1859, when it looked as though the Metropolitan Railway Company would be wound up with no line built, he <small>[Charles Pearson]</small> wrote a pamphlet: [...]. <WSD>Gadfly</WSD> he may have been, but by this 'letter' he persuaded the Corporation of London to invest £200,000 in the line, a most unusual example of a public body investing in a Victorian railway. 
Meaning of the word marked with <WSD> tags:  One who upsets the status quo by posing upsetting or novel questions, or attempts to stimulate innovation by proving an irritant.