Walter and Reimar Horten were teenage air enthusiasts in Germany between the World Wars - a time in which the Treaty of Versailles limited the construction of advanced airplanes, and in which German military flying had gone underground, taking the form of civil 'clubs' where students trained on gliders under the supervision of decommissioned WWI veterans.
This back-to-the-basics education, and an admiration of German avant-aircraft designer Alexander Lippisch, led the Hortens away from the dominant design trends of the 1920s and '30s, and toward experimenting with alternative airframes -- building models and then filling their parents' house with full-sized wooden sailplanes. The first Horten glider flew in 1933, when both brothers were still in their teens.
The Hortens' glider designs were extremely simple and aerodynamic, generally consisting of a huge, tailless albatross-wing with a tiny coccoon of a fuselage, in which the pilot lay prone. They were also beautiful -- simple to the last line, and iconic like an image of flight itself. But the great advantage of the Horten designs was the extremely low parasitic drag of their airframes. They were 'slick' and scalable to high speeds.
By 1939, with Hitler in power and the Treaty of Versailles no longer in effect, Walter and Reimer had entered the Luftwaffe as pilots. (A third brother, Wolfram, was killed flying a bomber over Dunkirk.) They were also called upon as design consultants, although they suffered a disadvantage in that their reputation was very much grass-roots, among Germany's aeronautical community, rather than through official connections.
The Hortens had made the natural leap to powered flight in 1937, with a twin-engined pusher-prop airplane (an earlier glider had a mule engine). The Luftwaffe, however, paid mostly lip service to their designs until 1942, when grudging (and partly under-the-table) support was given to a twin-turbojet-powered fighter design, designated under wartime protocols as the HO-IX.
Working turbojets were scarce in wartime Germany, and other projects carried higher priority. Although the turbojet-equipped HO-9 reached almost 500 mph in trials, the project was soon given over to the theretofore low-tech aircraft company, Gothaer Waggonfabrik, as the Gotha Go 229.
The Go-229 was a fighter with great potential, but arrived too late to see service. Among other advanced Horten designs of the 1940s was the supersonic delta-wing HO-X, designed as a hybrid turbojet/rocket fighter with a top speed of Mach 1.4, but tested only in glider form (as the HO-XIII), and later with a piston engine.
As the war ended, the Horten brothers emigrated to Argentina, where they continued designing and building airplanes. Reimar died in 1994, while Walter died in 1998.