"My dear Mr. President"

That's how Justice John Paul Stevens, who turns 90 this month, addressed the letter to President Obama in his resignation letter of today. Here's the Washington Post article:

[H]e will leave the court at the conclusion of the current term at the end of June. Stevens said he was announcing now so that the president would have time to make a nomination and the Senate to confirm in time for the start of the court's new term next October.
It will be Obama's second Supreme Court appointment after Justice Sonia Sotomayor, who was named last year to replace retiring Justice David Souter.
Stevens was appointed to the high court by President Gerald Ford, and joined the court on Dec. 19, 1975. His retirement is not a surprise and the White House has been preparing for the opening. Aides and Democrats close to the process name three people as likely frontrunners for the job: Solicitor General Elena Kagan, who Obama made the first woman to hold that post, and two appellate court judges, Diane Wood of Chicago and Merrick Garland of Washington.
Kagan and Wood were interviewed by Obama last spring before he nominated Sotomayor to the court.