Everithing started in 2007 with the original iPhone and with its iPhone OS, which was a bit ugly (in my opinion) and unstable but it was very intuitive! How has the iOS evolution been through the years? I’ll show you now!
As you can see in this picture this operating system changed its name into iOS because in 2010 Steve Jobs introduced the original iPad, and this iPad used the same OS as the iPhone but bigger. So the first iPad came with iOS 4.
iPhone OS -> i
Phone OS -> iOS
The four first OS versions brought incredible features with them. With Scott Forstall leading, iOS 5 and 6 didn’t bring many improvements except Siri. This improvements were totally needed because iOS was just the same every year. Until Scott was fired and Apple put Jony Ive (from the design department) ahead of iOS and this change could be seen when Apple presented iOS 7, iOS biggest change ever, in 2013. There are still some people that may not like iOS 7 design but it was obvious that iOS needed this because in 2012 Android was better than iOS in any sense. Jony has totally redesign the interface, now is clearer, with brighter icons and transparencies.
Finally, in 2014, Apple has introduced iOS 8, it’s not a change as big as the iOS 7 but iOS 8 adds some features that iPhones and iPads need.
Here’s a video made by the “the Verge” guys explaining iOS evolution. You may like it!