I think, marketers are invented "SEO" Its one of way is made for ..and google is help us to invent this strategy. When google was popular in the web so google launched In organic ranking by spending money on adward so exactly that point of time some of good marketeers made this strategy to getting rank by organic by following google guidelines. What do you think?
Veterans can get a stroll down memory lane here. This may cover the major ones but there were others.
Bruce Clay is the person who invented seo. and Leslie Rohde is one of the best seo analyst who create seo tricks
Even I am trying to find out who started, Initially.. Looking here and there... Some says google, Some says webmasters and some says yahoo... I believe there were few persons who initially started SEO, They didn't knew as what they are doing but they knew that the site will ranking and they are getting traffic and the imcome too, Then google realize this thing and give a name "Search Engine Optimization" Better knows as "Website Position Optimization" ... And months after, New and new techniques by webmasters and googles comes...
I guess its google and those two guys well no one actually invented it it just appeared as a system to find sites easier in my opinion and than later as more sites appeared it became more complex and got updated and so on