Gideon Mantell
Mantell did two things which were most important. He showed that the teeth of Iguanodon meant it must be a herbivore, and its shorter front legs meant it could be bipedal (walk on two legs). This was denied by Richard Owen, who did a good deal to hide Mantell's achievements. The discovery of this fossil is known to be the first evidence of a prehistoric reptilian dinosaur, dating back roughly 130 million years ago.