World War I was the first major conflict to feature the phenomenon of the ace - a fighter pilot who won acclaim by shooting down five or more enemy planes. The fact that aircraft failed to exist during any major conflict prior to WWI probably played a part in this.
When war broke out in 1914, it was only 11 short years since the Wright brothers had made their first faltering flight at Kitty Hawk. The aircraft of the day were slow, fragile and tended to fall out of the sky without too much persuasion - particularly if you lobbed a brick at them, which was the form of attack used by some early aces-to-be. Others tried bits of chain, grenades, pistols, and even swearing loudly, with varying degrees of success.
However, with the war stimulating technological progress, the aircraft and their weaponry rapidly improved. Before too long enemy fighters put themselves in greater danger than having one of their wings fall off and the engine ending up in the cockpit with them.
All the major countries involved in the war had flyers who became aces, but without doubt the most famous would have to be the German ace Manfred von Richthofen - more commonly known as the Red Baron. Together with his brightly-coloured squadron - known as the Flying Circus1 - they terrorised the skies above the Western front, although it has to be said they at least looked nice doing it. The Baron clocked up a record 80 kills before being shot down, either by a Canadian pilot called Brown, or some Australian anti-aircraft gunners, depending on who you believe. The Germans still claim one of his wings fell off and his engine ended up in the cockpit with him.
The second highest-scoring ace was a French guy called Fonck, but apparently he was arrogant and widely disliked, and not just by the 75 people he shot down, so despite being only five short of the Baron, no-one gives much of a Fonck about him these days.
The British also produced their fair share of aces, probably one of the more famous being Albert Ball. He only scored 40-something kills, so probably seems like small fry compared to Fonck and the Baron, but he once apparently took on 15 German planes in one day, shot five down, and then lived to tell the tale, so he at least gets the award for best display of suicidal insanity in a fighter pilot.
The highest-scoring American ace was Eddie Rickenbacker, a former race car driver, who could only manage to rack up 26 kills. In his defence it has to be said that the Americans were a little late crashing the whole WWI party, but Albert Ball once shot down 30 planes in three months, so it seems like a pretty poor excuse. Maybe it was because satellite/laser/infrared-sensing weapons weren't invented yet.
Many men from many different countries reached the coveted status of ace, and their effect on the course of the war and the hearts and minds of the public is inestimable. They fought and died in planes that most of us wouldn't send our dog up in, unless it happened to be one of those little rat-like ones with the flat faces, or unless of course you didn't like your dog, or it needed to be put down anyway, or if it was a dog that particularly liked flying, and had a death wish. Anyway, they were amazing people, and they paved the way for their evolutionary successors - the World War II fighter ace.