Complex sentence: Snowbound was the first horse to be ridden to an Olympic individual gold medal by an American rider, doing so with rider Bill Steinkraus in the 1968 Summer Olympics in Mexico City.
Split into simpler sentences: Snowbound was the first horse to be ridden to an Olympic individual gold medal by an American rider. Ridden by Bill Steinkraus, Snowbound had his gold medal win during the 1968 Summer Olympics in Mexico City.