Given his love of his investment role - we don't expect Buffett to step down while he is fit and well, but considering his investment genius his answer certainly merits attention.
Here are a few resources on these three kings:
This Economist article gives an excellent overview of Klarman's career
A transcript of a Ruane Cunniff & Goldfarb Investor day in 2009 includes contributions from Alexander among other members of the Sequoia team.
This legends of Value Investing video from Columbia Business School, recorded in Spring 2010, gives us a rare opportunity to experience a lecture from the man who manages Charlie Munger's money