Samsung is busy rolling out the new One UI to its flagships (including older models). It has been a long road getting here, so the company published an infographic detailing the key ideas that were introduced with each Galaxy S generation since the begging.
It starts with the original Galaxy S, but the first iterations of the current features landed on the Galaxy S III, which introduced S Voice the forefather of Bixby. Also, Smart Stay kept the screen from switching off while you were looking at it. The Galaxy S4 built on that and would automatically pause a video when you looked away. You could even scroll by glancing up and down.
The Galaxy S5 switched away from a skeumorphic to a flat design, the Galaxy S6 edge started the trend of curved screens. Heres the full infographic that covers every milestone since 2010: