On February 12, 1809, Charles Darwin was born. I think a strong argument could be made that Darwin is the most influential scientist of all time. He postulated that the complex biosphere we
observe is the result of understandable physical processes that we can study and observe at work throughout the long history of life on our planet. His contributions formed the basis for all of biology, and his keen insights provided the basis for understanding the nature of life around us.

“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Origin of Species, 1859

Oh, and some American president
was born on the same day, but he really is of minor importance compared to Darwin.