Where can I find the first version of linux operating system?

If you want to look at the history in a "nice" way, you could use Dave Jones's Linux-History Git repository, which includes all versions (at least all the versions that still exist, sadly some of the 0.99 versions have been lost forever) from 0.01 to 2.4.0. There is another history repository from Thomas Gleixner, which covers 2.4.0 to 2.6.12 and of course everything since 2.6.12 is available in Linus's Git repository. Linus also has a repository which contains an import of the CVS export of the BitKeeper repository from 2.5.0 to 2.6.12.

You can use Git's graft feature to glue these repositories together to get a unified view of the entire history. There are also various scripts floating around that try to make these repositories even more accurate, like this one for example.

It's discussed on KernelTrap. There's a good historical discussion, complete with release notes and mailing list discussions.

The linked article comes complete with this gem, which is undoubtedly what Linus looked like after release:

_{(source: kerneltrap.org)}

For the discussion, see here. For the complete Linux 0.01 release, download this and verify it with this signature.