Ralph Ellison wrote for 40 years without finishing his novel “Juneteenth.” Antoni Gaudí labored 43 years on the Sagrada Família basilica in Barcelona, but construction continues today. And in the annals of grand quixotica, Ehsan Yarshater also deserves a prominent chapter. At 53, he embarked on his magnum opus, a definitive encyclopedia of Iranian history and culture. At 75, he started looking for a successor. He didn’t find one so he kept going himself. Now he’s 91. He’s up to “K.” “My mission is to finish the encyclopedia,” he said recently from his office at Columbia University’s Center for Iranian Studies. He knows he won’t be able to do it personally, especially since the task keeps expanding as progress is made. There are topics to be added and entries to be updated. So Mr. Yarshater has tried to make sure the work will continue by establishing a private foundation with a $12 million endowment and finally choosing three scholars to replace him as general editor. >>>