A Guide to the Stereotypical Figures in the Equestrian World:
The Pony Clubber: Someone who attends Pony Club. Typically a rich little brat who thinks they can ride. They are more annoying when they can. They have the $5,000 horse, the $1,000 saddle, and rugs, bridles and boots to match. The other type of Pony Clubber is a teenager who works three jobs and attends school in a desperate attempt to keep their horse, who is a bugger to ride because he's too old to move. But he was all she could afford so she'll have a smile on her face.
The Classical Dressage Queen: Slow, methodical, they believe in the old way of training. Their house is filled with aged, yellow books and are obese from the amount of bookmarks stuffed in them. They will never use something that seems "modern" unless they found proof that something like it was used by the masters.
The Other Sort of Dressage Queen: They don't have grooms. They have servants. They are the very image of a true princess. This is what the rich Pony Clubbers tend to grow into. They're the sort that you would never approach without introduction, and then you would probably be afraid to speak to them unless spoken to first.
The Eventer: You do not mess with these people. They are as close to insane as you will get without actually being insane. They gallop horses over jumps which are huge and if they fall off and break three ribs and dislocate a shoulder they simply get back on and finish the course. And the only quote you will get from them after is "I got three time faults! Argh!" But most of them are experts at riding with one arm in a sling, and they'll never say die.
The Natural Horseman: Is like the Classical Dressage Queen in that they have books everywhere. They also use gentle methods, do not use "modern" things like spurs and believe everything comes from short sessions of gentle persuasion.
The Show Jumper: Another grown-up Pony Clubber, but this one has never learnt how not to rely on instructors for help. Still, their horses are generally well bred and they know what they're doing. And they're very good at getting off to re-make a jump after its been knocked down. They've turned it into an art.
The Jockey: Short. Thin. They never eat, but they know how to ride. Balanced precariously atop a mountain of muscle that can reach speeds of 40 miles per hour (64 km/hr), it's as though they are steering a car with nothing more than two easily broken pieces of leather. Jockeys know no fear.
The Cowboy/Stock Rider: These guys know horses in every way the others don't, because they are with their horses all the time. Their horse is the very model of a perfect "bombproof" horse, but you wouldn't put your kid on one, because if they see a cow separated from the herd, they can run like hell. And the rider, somehow, will not come unstuck even after the most violent bust of energy. These people are also female; think of a cowgirl.
The Rodeo Rider: A long arm of the cowboy tradition, they are highly skilled people who are either dead/dying in a week or they'll be in the trade for years to come. Perhaps they are glory seekers, perhaps they romanticize the dust and sweat and danger, but I can say one thing in all confidence: they know how to stay on a horse. (Inserted due to wertperch's suggestion.)
The Pleasure Rider: They dabble in everything, and ride everything, though not always willingly. Born of the spirit of the poor teenage Pony Clubber they can be seen at the dressage, the shows, the hacks and the jumping competitions. They also come from the less serious of the above who get married, settle down and have children.
Note: In Australia about 70% of all horse riders are female, and in the US, 128 in every 100,000 participants in horse racing die.