The Mathematics Genealogy Project is a wonderful thing. Here is a personal application: I studied with David Griffeath. (I'm not in the database because my degree ended up being in physics, not math.) David studied with Frank Spitzer, who studied with Donald Darling, who studied with Morgan Ward, who studied with Eric Temple Bell, who studied with F. N. Cole, who studied with Klein, who studied with Lipschitz, who studied with Dirichlet, who studied with Poisson, who studied with Lagrange, who studied with Euler, who studied with Johann Bernoulli, who studied with Jacob Bernoulli. [Via Stephen Laniel's Unspecified Bunker.]