August 18, 1903, a month prior to the successful Wright Brothers flight, Karl Jatho claimed to have successfully flown.
The flight  was more a lurch, hop, and a jump rather than a flight. 

Flight attempt took place in  Hanover, Germany. 
DISTANCE: 18 meters and managed to reach 1 m above ground, which is generally not considered a full controlled flight. He flew his own design, a pusher biplane powered by a single-cylinder 9 h.p. Buchet engine.

No stamps have been issued for Jatho, so to honour his pioneering flight attempts enjoy an early airmail from Germany.

Flying Post Horn
Issued by the Imperial German post office in 1919
Designer: Georg Alexander Mathéy

Jatho founded Hannoversche Flugzeugwerke GmbH 1913, which went  bankrupt shortly after war WW1 broke out. there was little interest in his designs by the war ministry, cutting Jatho  off much needed war contracts. Without an influx of money, he was forced out of business. 

The Jatho rarely gets mentioned in books/articles as a first flight. There is debate whether his first flight was a controlled one or a “jump flight”.  However, Jatho claimed, after the Wright Brothers success to have flown a few flights prior to Kitty Hawk. He never presented documentation nor did witnesses at the 1903 flight come forward. The majority of historians don’t accept Jatho’s claims.

A few witnesses came forward decades after the flight and claiming they witnessed a successful flight.  Doubt was cast on their late claims, for two reasons:

1. why hadn’t they come forward when the event occurred

2.  the testimonials were viewed as nothing more Nazi propaganda attempts to boost German prestige. 

You can see more pioneer flights here Aviation – firsts, stamps and more 
The Jatho Biplane and a Challenge to the Wright Brothers — On Verticality has an entertaining page on Jatho.