Who are the authors of the pure Linux kernel from scratch, which was integrated with GNU tools and formed the full GNU/Linux Operating system in the 1990s? I have read some wiki articles but I haven't got any clear cut idea on the history.
The wikipedia page has a fairly clear history. Linus Torvalds, then a student, wrote his own kernel in the summer of 1991 because he was unhappy with the available Unix kernels: Unix itself (with the Bell Labs code) was extremeley expensive (even PC unices such as Xenix), there was Andrew Tanenbaum's MINIX but it was only available to purchasers of Tanenbaum's book, and Torvalds was unaware of the effort led by Berkeley University to produce a free Unix (BSD), and BSD didn't run on PCs yet at the time.
Since then, thousands of people have contributed to the kernel, most of them in the form of drivers.
Richard Stallman, father of the GNU Project
The real story is :
Year 1991 :
DOS brought by Bill Gates was reigning the world of personal computers. The other player in the personal computer world was UNIX by Bell Labs, but it was extremely expensive and the source was not publicly available.
Then there was the MINIX by Andrew Tanenbaum, which was not a superb OS but made the source code was publicly available. Tanenbaum captured the souls of computer science with the elaborate and lively discussion of the art of creating a working OS. Students of Computer Science all over the world went through the book, reading through the codes to understand the very system that runs their computer, and one of them was Linus Torvalds.
The GNU project created a lot of the tools line GCC, etc. but still there was no OS.
For rest of the story and how Linux was written please read through the following link.
Linux History Time line :