(4) Aristotle vs. (5) Marie Curie
Aristotle's academic lineage alone is enough to get him into the tournament. He was Plato's brightest pupil and tutored a young Alexander the Great. It wasn't just who Aristotle knew, though, it was what he knew. With a seemingly boundless enthusiasm for any number of subjects, Aristotle made major breakthroughs in philosophy, physics, biology, chemistry, and ethics. On top of that, he pioneered both formal logic and zoology. If you were in Greece in the fourth century B.C. and had a question about pretty much anything, you knew whom to ask.
(5) Marie Curie
Science's undisputed first lady has a C.V. that may never come along again. Along with her husband Pierre, she discovered the chemical elements polonium and radium. The tag team also discovered radioactivity, which netted her the 1903 Nobel Prize for Physics. Even after Pierre's death in 1906, Marie kept working and eventually isolated pure radium, which won her the Nobel Prize for Chemistry in 1911. Her name is still synonymous with radioactivity, a word she coined. Even more impressive: she did it all as a working mother.
Aristotle's theories may not have always held up so well "“ he'd probably love another crack at that whole geocentric universe thing "“ but he helped look at so many branches of science and philosophy with a special focus on reason that it's hard to fault him for it. (After all, some of the scientific facts we cling to as hard truths now will surely seem laughable to people in several centuries.) Curie, though, gets points for accuracy, for giving birth to another Nobel Prize winner, and for helping usher in the atomic age. Curie's already blown up Linus Pauling, and Aristotle jumped over Evel Knievel to make it this far. Who's going to make it to the next round, though?
[See the whole bracket here.]