Mo Williams, the high-scoring point guard from Milwaukee, will go to Cleveland in the deal.
The 6-foot-1 Williams averaged 17.2 points and a team-high 6.3 assists for the Bucks last season.
"Acquiring Mo strengthens our nucleus of players for both the short and long term. He is entering his prime NBA years and will be part of the foundation of our future success," Cavaliers general manager Danny Ferry said in a statement. "His ability to push the tempo, get inside the lane, shoot from the perimeter and distribute the ball will be very valuable for us."
Ferry said the team let James know of the deal even though he's on the other side of the world.
"We've communicated with most of the team," Ferry said. "All these guys are very excited. They respect Mo as a player, and they're looking forward to playing with him."
Oklahoma City, formerly known as the Seattle SuperSonics, also gets Desmond Mason, the athletic small forward, from the Bucks.
Since joining the Cavaliers in 2003-04, James has not had a teammate who averaged as much as 17 points per game. But Williams has done so the past two seasons, averaging a career-high 17.3 points in his breakout season of 2006-07.
The Cavs have long sought a scorer to take pressure off James, who led the NBA last season with a 30.0 scoring average.
James' lack of help was particularly noticeable in Cleveland's Game 7 loss to Boston in the Eastern Conference semifinals when he scored 45 of the Cavs' 92 points.
Larry Hughes was supposed to be James' sidekick, but couldn't fulfill the role and was sent to Chicago last year at the trade deadline in a 10-player deal.
In Beijing for the Olympic Games, James gave his vote of approval for the trade.
"It can help us. I think Mo is a very good point guard, he can create for himself and create for others, so it's a great move. I think it's an 'A,' " he told ESPN.com's Chris Sheridan.
"I think this is a move to be able to get a talented, young, 25-year-old point guard that can be part of the future," Ferry said.
Williams' agent, Mark Bartelstein, said a scoring-minded point guard will make it easier on James and sharpshooter Daniel Gibson.
"I think there was so much pressure on LeBron to create so much of the offense in Cleveland," Bartelstein said. "I think somebody like Mo is going to really make the game easier for LeBron and create opportunities for other people."
Mason played in college at Oklahoma State and spent time with the Hornets franchise in Oklahoma City when it was relocated after Hurricane Katrina.
"We're excited," said Mason's agent, Roger Montgomery. "He's been to Oklahoma City, he's familiar with the people there, he's familiar with the Ford Center, he's played there, the fans loved him when he was there. His nickname is the Cowboy. It's really apropos to come back."
Oklahoma City general manager Sam Presti sees the basketball benefits.
"We understand that it's a unique opportunity here specifically but we've got to do the best thing for our basketball team, and we feel like the best thing for our basketball team is to add some toughness and some intangibles defensively for us at that position," Presti said. "It just seemed like the right fit for us."
Ridnour, who averaged 6.4 points and four assists last season as the backup to Earl Watson in Seattle, had faced decreased playing time in Oklahoma City after the franchise drafted point guard Russell Westbrook with the fourth pick.
Bucks general manager John Hammond said he can envision Ridnour thriving in Milwaukee.
"His most productive days in the NBA were just a few short years ago when he had Ray Allen on one wing and Rashard Lewis on the other wing," Hammond said. "Here, you say you have Michael Redd on one wing and Richard Jefferson on another wing, you're putting Luke Ridnour in the best possible position to be successful again as he has been in the past."
Griffin averaged 1.9 points in minimal playing time after coming over from Chicago in a midseason trade.
The acquisition of Williams may spell the end of Delonte West's brief tenure in Cleveland. The Cavaliers have been embroiled in contract talks with West, a free agent who became their starting point guard after being traded from Seattle last February.
While Williams, 25, will definitely be Cleveland's starting point guard, a person close to the situation said the Cavaliers still will look to re-sign West, a 6-foot-4 combo guard who could start beside Williams in the backcourt.
Milwaukee and Oklahoma City view the trade largely as a salary dump.
The Bucks, who traded former lottery pick Yi Jianlian to New Jersey for Jefferson earlier this summer, get rid of the five years, $43 million left on Williams' contract while taking on Jones and Griffin, both of whom are in the last year of their deals. Ridnour has just two years, $13 million remaining on his contract.
It's also the next step in an offseason facelift in Milwaukee by new general manager John Hammond. The Bucks fired coach Larry Krystkowiak after going 26-56 last season and replaced him with Scott Skiles. They also selected West Virginia forward Joe Alexander with the eighth pick in the draft.
"Our challenge from Day One has been to shape our roster in a way that our fans will see a team that is competitive, that plays hard every night and has a chance to win," Hammond said. "We feel this trade continues to move us toward that goal for this season and beyond."
As for Oklahoma City's acquisitions, Smith and Mason also are in the final year of their deals.
Chris Broussard is a writer for ESPN The Magazine. Information from ESPN.com's Chris Sheridan and The Associated Press was used in this report.