TITLE: PhD dissertations that solve an established open problem
QUESTION [61 upvotes]: I search for a big list of open problems which have been solved in a PhD thesis by the Author of the thesis (or with collaboration of  her/his supervisor).
In my question I search for every possible open problem but I prefer (but not limited) to receive answers about those open problems which had been unsolved for at least (about) 25 years and before the appearance of the ultimate solution, there had been significant attentions and efforts for solving it. I mean that the problem was not a forgotten problem.
If  the  Gauss  proof  of  the  fundamental theorem of  algebra did  not had  a 
 gap,  then   his  proof could  be  an important example of  such  dissertations. 
I ask the moderators to consider this question as a wiki question.

REPLY [13 votes]: Does Serre's (Jean-Pierre) thesis qualifies ? He computed there a lot of homotopy groups of spheres. But I don't know how old was this problem in 1951.