Ed Kleinbard, my once (at Cleary Gottlieb) and future (when he too becomes a tax prof) colleague, is leaving the JCT on May 15. See BNA DTR Apr. 22, 2009 (speculating wisely about a possible successor as well).
Stepping into his shoes will be current deputy chief of staff Thomas Barthold, who has been at JCT for two decades and served as acting chief of staff (appointed by Republicans Bill Thomas and chuck Grassley) from November 2005 through September 2007, see here.
Just who is Barthold and what does he bring to the table? Barthold holds a PhD in economics and has roots in academe, having started out as a teaching fellow at Harvard and then an assistant professor of economics at Dartmouth. See resume. Over his career he's written a good bit on capital gains and estate taxes. For example, in a 1991 paper with Takatoshi ito, Bequest Taxes and Accumulation of Household Wealth: U.S. - Japan Comparison, he concluded that a substantial portion of wealth is bequethed from one generation to the next in both countries. But Jay Soled at Rutgers didn't think much of Barthold's statement that an IRS study of tax cheating in 2001 suggested that the majority of capital gains cheating was done by "Joe Sixpack"--i.e., taxpayers with taxable incomes of about $30,000 (or incomes before deductions of less than $50,000). See this story on "surprising finding in capital gains study", New York Times, May 5, 2007. That's because those lower-income taxpayers earn only about $15 billion of the total of $471 billion of long term capital gains reported in 2004--most of the capital gains accrue to the very wealthy, with about 10,000 taxpayers earning more than a third of all profits from investment sales. Soled's own study and a more thorough 1979 IRS study didn't agree with the Barthold results.
Rangel, whose office announced the appointment on Wednesday, noted the committee's gratefulness to Barthold "for his continued service, expertise, and leadership."