Supreme Court Justice John Paul Stevens announced Friday he will be stepping down from his post, which will allow President Barack Obama to name a nominee for the second time in his presidency.

Stevens has served as a Justice since 1975, and he has been known in recent years as being one of the court’s more liberal voices.

“Having concluded that it would be in the best interests of the Court to have my successor appointed and confirmed well in advance of the commencement of the Court’s next term, I shall retire from regular active service as an Associate Justice,” Stevens wrote in the letter to Obama announcing his retirement.

His retirement will be effective after the court adjourns for summer recess around the last week of June.

In a statement praising Stevens’ career, Obama said he has served as an ?impartial Justice of the law,? since he joined the court.

“He has worn the judicial robe with honor and humility. He has applied the Constitution and the laws of the land with fidelity and restraint,” Obama said in the statement. “His leadership will be sorely missed, and I just had an opportunity to speak with him and told him on behalf of a grateful nation, that I thanked him for his service.”

Obama said it would be in the Supreme Court’s best interest to have Stevens’ successor approved before the next term, and he views this choice as one of his most serious responsibilities as president.

University of Wisconsin political science professor Howard Schweber said he believes Stevens’ age is driving his decision to step down, however the timing of it may be due more to political reasons.

Stevens will turn 90 in less than a month.

“His legacy will be one of a very thoughtful justice who reasons very carefully,” Schweber said. “He was an excellent writer and sophisticated legal reasoner.”

At the beginning of his career, Stevens started out as a more conservative voice, and he has maintained that the court itself has become more center-right over the years and is not a case of him becoming more liberal.

Schweber said it is probably a combination of the two, as the “ideological center” of the court shifted toward the right during the Rehnquist years.

U.S. Solicitor General Elena Kagen is generally viewed as the front-runner to take over Stevens’ spot, Schweber said, not only for her strong qualifications, but also for her history of reaching out to both conservatives and liberals. Kagen also does not have many writings on controversial subjects, which could make her confirmation process easier.

Sen. Russ Feingold, D-Wis., also had praise for Justice Stevens and said he looks forward to engaging senators from both parties during the next nomination process.