This mutual fund manager has staying power. Mairs and Power's two flagship funds -- Mairs and Power Growth Fund (opened in 1958) and the Mairs and Power Balanced Fund (1961) -- have some $2 billion in assets under management. The firm also manages about $3 billion in assets for retail customers, benefits managers, and charitable foundations. Mairs and Power relies on a conservative investment strategy, where it seeks growth stocks that it holds for long periods of time. It invests heavily in companies based in the Midwest, where the firm is based, because of its familiarity with the region. George Mairs, Jr. founded the firm in 1931, and George Power joined in 1944.