Ruben Sierra is a changed man, at least according to Jorge Posada.

“He has a great attitude right now,” Posada said of Sierra, who had an RBI double in the Yankees’ 5-2 win over the Cardinals yesterday. “A different attitude than I saw in ’95-96. He is a lot different. He understands his role. You see him smiling around and having fun.”

After leaving Yankee Stadium in ’96, Sierra has played in 12 locations, including Cancun, Mexico, and Atlantic City, which sounds a lot more luxurious than it really is for a baseball player.

In ’99, he didn’t play in even one major-league game, toiling instead in Atlantic City as just another has-been.

While Sierra’s attitude has changed – at least, according to Posada’s observances over a little more than a week back at the Stadium – his desire to return to what he once was remains.

“I want to let people know I can be a superstar again,” the 37-year-old Sierra said.

Since the Yankees re-acquired him on June 6, Sierra has put up superstar numbers, going 8-for-19 with two homers and four RBIs. Most importantly, he’s done it with a positive attitude.

In his first go-around with the Yanks, Sierra caught Torre’s ire to the point that the skipper went out of his way to rip Sierra in his book.

“When he left, after he bounced around, he was auditioning in spring training,” Torre said. “He knew he had to work hard to get back and understand you can’t take your ability for granted. He is blessed with amazing ability.

“He can hit from both sides of the plate, like Clemente. He wears 21, you would think [Clemente] was his idol.”

Clemente is Sierra’s idol. He wears No. 21 to honor his fellow Puerto Rican. While the Hall of Fame – once a hopeful reality in Sierra’s early years – is now a fleeting memory, the chance to excel in the big leagues is not.

“I don’t take anything for granted now,” Sierra said.

While Sierra’s goal is to be a superstar again, his role seems relatively small. When Nick Johnson returns from the DL, Sierra will have trouble finding at-bats unless he continues to hit like he has.

“I believe in myself,” Sierra said. “I know I can play and can be a superstar again. From now on, that is what I want to do and let people know that I’m a superstar again.”

That is the hope, but Sierra understands his role right now.

“I always try to stay ready and sharp for any kind of situation and don’t let anything bother me,” Sierra said.