apparently the Smithsonian agreed to never recognise any other potential first flight pioneer in exchange for the Wright's plane. Dundee claims an early flying pioneer, possibly the first in UK, maybe the world.
http://www.thecourier.co.uk/news/history-2.1462/is-history-right-or-was-dundee-s-preston-watson-the-first-to-make-a-powered-flight-1.718839
Loadsa people flew before the Wrights 'first' flight, including both of the Wrights (gliding). Some of 'em even did so (briefly) in powered craft. The Wrights' claim depends on a few qualification to 'first flight', e.g. powered, controlled, took off under own power. It seems pretty certain that their 'first' flight was closer to achieving all of those at once than any previous flight, but it was just one step among many.
To me, their achievements were significant, but I'm not sure that they made any net contribution to aviation. Their insane patent war* held back the progress of aviation in the USA**, & the world was filled with experimenters & theoreticians at the time. It was going to happen, & soon, whether the Wrights existed or not.
*They claimed that any kind of control mechanism which changed the shape of a wing, whether by warping, ailerons, or any other means, was covered by their patent. Patently ridiculous, since wing-warping & ailerons had been in the literature for decades, had been used on experimental gliders, & there was even a prior patent (British, expired) for ailerons.
In one of my varied ‘book jacket’* of careers I used to work at the Science Museum in London and part of my job was to do guided tours of some of the galleries, including the flight gallery, in which there is a replica of the Wright Flyer – but the Science Museum actually used to have the original aircraft on display.
At first the Smithsonian did not recognise the Wright brothers as having made the first powered flight. So much so that the Wrights donated the Wright Flyer to the Science Museum in the UK instead, where it remained until 1945. The agreement the Smithsonian made referenced in the article occured in 1939 if I remember right, after the Smithsonian contracted to agree the Wright Brother’s claim in order to receive the Flyer.
The outbreak of war prevented the safe transport of the Flyer back to the US and the Science Museum made a full scale replica before giving it to the Smithsonian in 1945 after the end of WWII.
*Two more jobs and I’ll have that long list of varied jobs that lots of authors seem to have. I’ve driven a train, worked in a chocolate factory and been Maureen Lipmann’s paperboy amongst other things.