Have the idle rich replaced the working rich at the top of the U.S. income distribution? Using tax data linking 11 million firms to their owners, this paper finds that entrepreneurs who actively manage their firms are key for top income inequality. Most top income is non-wage income, a primary source of which is private business profit. These profits accrue to working-age owners of closely-held, mid-market firms in skill-intensive industries. Private business profit falls by three- quarters after owner retirement or premature death. Classifying three-quarters of private business profit as human capital income, we find that most top earners are working rich: they derive most of their income from human capital, not physical or financial capital. The human capital income of private business owners exceeds top wage income and top public equity income. Growth in private business profit is explained by both rising productivity and a rising share of value added accruing to owners.