The Dynabook was one of the first tablets during the 1970s. It had an integrated Keyboard and looked similar to tablets today.
It was again Apple who developed the Newton MessagePad in 1993. It was the precursor of very popular PDA's later those years.
A few years later, after Apple presented their iPhone in 2007, the first generation of iPads in 2010 were released. Today tablets are multifunctional, transportable mini-pc without keyboards.