"We're thrilled to be able to make this trade," Red Sox general manager Theo Epstein said Monday at a news conference introducing the slugger, adding that the team has admired the power-hitting Gonzalez since his days playing for the Texas Rangers.
The Red Sox made a run at Gonzalez before the 2009 trading deadline and again last season, Epstein said.
Gonzalez, donning a Boston jersey without a number, said the Red Sox have always been his favorite American League team in part because of Boston icon and Hall of Famer Ted Williams, who like Gonzalez, was a left-hander and San Diego native.
"I'm very excited to be in Boston and ready to beat the Yanks," he said.
The Red Sox sent minor league right-hander Casey Kelly, first baseman Anthony Rizzo, outfielder Reymond Fuentes and a player to be named later to San Diego.
Gonzalez is entering the last year of his contract in 2011 and although the trade does not include a contract extension, Epstein said he's "confident" something will be worked out.
"We're going to try to get something so he will be here for a very long time," said John Boggs, Gonzalez's agent.
In five seasons with San Diego, Gonzalez has 161 homers and 501 RBIs. Including parts of two seasons with Texas, he has 168 homers and 525 RBIs. He hit .298 with 31 homers and 101 RBIs last season.
Epstein expects better numbers in Fenway Park with the Green Monster in left field. "We think he is going to wear the wall out," Epstein said.
Gonzalez had surgery to clean up the labrum in his non-throwing right shoulder on Oct. 20, but he said Monday he's ahead of schedule and expects to be ready for Opening Day.
"I'm very excited to start this new phase and look forward to a lot of world championships," he said.