This probably occurred to a lot of people who had the misfortune of watching Star Wars: Revenge of the Sith:
If we accept all the Star Wars films as the same canon, then a lot that happens in the original films has to be reinterpreted in the light of the prequels. As we now know, the rebel Alliance was founded by Yoda, Obi-Wan Kenobi and Bail Organa. What can readily be deduced is that their first recruit, who soon became their top field agent, was R2-D2.