Einstein was a theoretical physicist who developed equations that successfully linked the deeper properties of space, time, mass and energy. He was the first to move physics beyond the classical realm of Newton, starting in 1905. He was the epitomy of "post influence of Newton".
If you walk at 10 mph along a train running at 50 mph you are walking at 60 mph relative to the ground. But this relationship breaks down progressively as you approach the cosmic speed limit of light.