I'd say it's a commonly held belief that the Wright brothers were the first to achieve controlled, powered and sustained heavier-than air human flight, as it can be found in most history books. However, there are many who say that this might not be so....
The most notable man claiming to have flown before the Wrights was Gustave Whitehead, who is purported to have designed, built and flown his own craft approximately two years before Orville and Wilbur Wright.
"Two years, four months and three days before the successful flights of the Wright brothers at Kitty Hawk, a birdlike monoplane took to the air at early dawn on August 14, 1901, near Bridgeport, Connecticut, carrying its inventor and builder, Gustav Whitehead, a distance of approximately a half mile." Stella Randolph, The Lost Flights of Gustave Whitehead. source
An article from the New York Herald dated August 19, 1901 is quoted as saying:
Mr. Whitehead last Tuesday night, with two assistants, took his machine to a long field back of Fairfield and the inventor; for the first time flew in his machine for half a mile. It worked perfectly, and the operator found no difficulty in handling it Mr. Whitehead's machine is equipped with two engines, one to propel it on the ground, on wheels, and the other to make the wings or propellers work.
However, while this sounds quite convincing, an article from Scientific American dated 1901 perhaps sheds some light on why Gustave Whitehead is not known today as the first aviator:
"A novel flying machine has just been completed by Mr. Gustave Whitehead, of Bridgeport, Conn., and is now ready for the preliminary trials. Several experiments have been made, but as yet no free flights have been attempted".
Could be that the Wrights were the first to achieve flight, even though Whitehead's machine may have been built earlier?
More than one source offers this simpler explanation; that there was simply no evidence to back Whitehead's claims:
He continued building and experimenting with airplanes, and his supporters claim that he made powered flights in both Pittsburgh in 1899 and Bridgeport in 1901 and early 1902. His letters to periodicals and interviews in newspapers claim powered flights as early as 1898 and as late as 1903. He was, in fact, one of a several turn-of-the-century experimenters who regularly issued press releases that described successful flights with no real evidence to back his claims. Whitehead made his last airplane in 1908 — which did not fly — then went on to build helicopters which did not fly
Research into the topic can yield credible-sounding claims for either side, and my current position can be summed up by this particular quote I happened across at flyingmachines.org:
"That Whitehead designed and built (and flew) gliders and designed and built powered flying machines is not in dispute. That any of his heavier-than-air powered machines flew is."
Is there credible evidence proving Gustave Whitehead achieved powered heavier-than-air human flight before the Wright brothers?