I'm horrible with names and details, so bear with me.
In some other world/universe some arbitrary period of time in the past/future, a new species of monstrously large quadrupedal animal was discovered. The [insert species name] was discovered to be incredibly fast for its size, but it was also found that it particularly enjoyed the taste of humans. After various irrelevant events and incidents that aren't all that important, some of these beasts were captured, and someone had the equally bright and insane idea to use them for transportation. Unfortunately, the only way the [insert species name] could be motivated to run was using the promise of human flesh. A good deal of money was offered for people to act as bait, but obviously there weren't many volunteers.
But the greedy/insane/suicidal guy you see here is one of them. He's equipped with a protective suit and helmet that is brightly colored to keep the [insert species name]'s attention as well as thick enough to save at least a few of his vital organs from a tooth or claw puncture.
The chariot rider is wearing a historic-pilot-styled helmet since that's pretty necessary when moving at 130 miles per hour.