Top Indian-American lawyer Neal Kumar Katyal will now serve as US government's top legal counsel, with Solicitor General Elena Kagan vacating the post following her nomination to the Supreme Court. Kagan informed the Supreme Court in a letter that she has been nominated by President Barack Obama for the vacancy in the apex court, and the development leaves her principal deputy Katyal to serve as the Acting Solicitor General. Solicitor General is the top US lawyer, who argues the administration's cases before the Supreme Court. One of the country's top legal brains and the son of Indian immigrants, Katyal's promotion was effective as of May 10, the date Obama nominated Kagan as replacement for retiring Justice John Paul Stevens. Katyal, 40, previously served as National Security Adviser in the Justice Department in 1997-1999. In one of the most notable cases, Katyal representedSalim Ahmed Hamdan, the driver for Osama bin Laden, and successfully challenged the president's authority to create military commissions to try Guantanamo Bay detainees without legislative authority. Katyal also suggested that a new federal court should be created to try terrorism suspects at Guantanamo Bay.