Many great mathematicians and physicists had used time as 4th dimension, but none developed it out into special relativity, even Lorentz has his name on the Lorentz's transformation, but he didn't see a brand new space-time relationship. There is a huge gap between linking something together to writing it down with a mind boggling and fundamentally new theory to reshape how human beings see the universe. That said, all people's work are built on top of predecessors. Without generations work on mathematics before 20 century, Einstein wouldn't have developed GR as well.