The under-appreciated Wegener - what a man!
Continental drift - a concept before its time.....
Had a flash of intuition, gathered lots of circumstantial evidence, was heartily laughed out of town in 1915 by just about everyone, and turned out to be spang-on (even if he didn't understand how it worked)
A triumph, and relevant today in modified form to studies of Europa and (probably)upcoming Enceladus at Saturn.
His idea must figure in the top 100 'eureka' moments.