(Reuters) - Four-time All-Star Joe Nathan signed a two-year contract to become the closer for the Texas Rangers, the back-to-back American League champions said on Tuesday.

Financial terms of the deal were not disclosed but a report on the Rangers website said Nathan agreed to a $14.5 million contract with a $9 million option for 2014.

Rangers General Manager Jon Daniels said signing the former Minnesota Twins pitcher allows the team to shift promising closer Neftali Feliz into the starting rotation.

"We're getting a guy with big-time makeup, big-time pedigree and big-time stuff in Joe Nathan and also moving one of the best arms in professional baseball to the rotation," Rangers General Manager Jon Daniels said late Monday.

Nathan missed the 2010 Major League Baseball season after elbow surgery but returned in 2011 and appeared in 48 games, posting a 2-1 record with a 4.84 earned run average.

"This club is a perfect fit for myself and my family," Nathan told a news conference on Tuesday, his 37th birthday.

Nathan said the success of the Rangers, World Series finalists the past seasons, was a big reason for his decision to sign.

Although he struggled early last season with Minnesota, the right-hander said he improved as the season progressed and expects to be better in 2012.

"Guys who have been through this told me 18 months was the key. That was the beginning of the offseason for me. I feel if I can get through the offseason with a good workout, I expect to feel even better in spring training," said Nathan.

Feliz said he welcomed the decision to make him a starter.

"I was a starter for my whole career before I came to the major leagues," the 2010 American League rookie of the year and All-Star said in a statement.

He had 32 saves and a 2-3 record for the Rangers in 2011, but gave up a two-out two-run triple in the ninth inning of Game Six of the World Series, which the St. Louis Cardinals went on to win in seven games.

(Reporting by Gene Cherry in Salvo, North Carolina; Editing by Frank Pingue)