Baker was being looked after by Shield's brother, who found him Saturday morning. Shield said Baker was ill for years with a lung condition.
She also said her uncle -- who was 3 feet, 8 inches tall -- did not expect to "live past his teenage years because he was a 'little person,' so it is pretty amazing he lived this long."
Baker died in his sleep Saturday morning, according to his nephew and caregiver Andrew Myerscough.
That was Baker's wish -- to go peacefully, his nephew said. "I couldn't ask for more."
Up until his final moments, Baker was in good spirits and was watching the Olympics on television, Myerscough said.
'An inspiration to many'
But the actor's family watched him deteriorate for years because of respiratory problems.
"I cared for him every day," Myerscough said. "He was a huge part of my life and I'm going to miss him."
"He was an inspiration to many people -- he never let his disability affect or stop him from doing anything he wanted to do."
Baker was best known for the robot character he first played in 1977's original "Star Wars."
"Baker created Artoo's (R2's) much-loved innocent yet adventurous personality from inside the droid," said a statement on the official Star Wars Twitter account.
"Whether it was the slow turn of Artoo's dome to convey suspicion or nervous wobbles signifying fear, Baker made a robotic being seem very human."
Baker also played Paploo the Ewok in 1983's "Return of the Jedi. "
"I have had a fairly quiet year, and when the sunshine has allowed I have enjoyed the peace and tranquility of my garden," Baker wrote on his website.
'Heart and soul of R2-D2'
He was fondly remembered across the entertainment world on Saturday.
"Kenny Baker was a real gentleman as well as an incredible trooper who always worked hard under difficult circumstances," Star Wars creator George Lucas said in a statement.
"A talented vaudevillian who could always make everybody laugh, Kenny was truly the heart and soul of R2-D2 and will be missed by all his fans and everyone who knew him."
Screenwriter Brian Lynch tweeted: "Rest in Peace, Kenny Baker. Thanks for bringing my favorite STAR WARS character (and 1st STAR WARS figure) to life."
British actor Rahul Kohli said in a post: "You brought life to one of my favourite characters, thank you Kenny Baker. Rest in peace."
Actor Kevin Smith wrote on Twitter, "Rest in Peace @starwars legend #KennyBaker - whose name I learned at age 7 because he brought #R2D2 to life. Feels like losing family..."
Daniel Logan, who played Boba Fett in "Star Wars: Episode II" and "Star Wars: The Clone Wars," tweeted: "So sad to hear one of my dearest friends passed away. Rest in peace Kenny Baker. Love you. Will miss you!"
'Put the lid on me like a boiled egg'
Baker played R2-D2 in "The Empire Strikes Back" and "Return of the Jedi," as well as the three "Star Wars" prequels from 1999 to 2005.
In an interview on his website, Baker said he initially turned down the role that would define his career.
He recalled telling Lucas, "I don't want to be stuck in a robot. What for, for goodness' sake?"
But he relented: "I said, 'I'll help you out, I'll do you a favor.' He said, 'You've got to do it. We can't find anyone else. You're small to get into (the robot costume) and you're strong enough to be able to move in it.' And they couldn't use kids."
Baker added, "I could work all hours, from 8 in the morning to 8 at night. You couldn't do that with kids. I was a godsend to them really. They'd made the robot in rough form and I was the only one around at the time that was just right for it. I got into it and they put the lid on me like a boiled egg."
The actor told CNN in 1999 that he didn't think the original "Star Wars" film would take off.
"We all thought, 'What a load of rubbish. This is going to be a non-event,'" he said. "How wrong we were."
And wobbling around in a metal costume -- which was heavier than he was -- in the 100-plus degree heat of Tunisia wasn't easy, according to Baker.
"The thing weighed about 80 pounds," he said. "I weighed 70 pounds."
'Overcome my height difficulties'
Baker also appeared in a number of other films in the 1980s, including "The Elephant Man," "Time Bandits" and "Flash Gordon."
In 1978, Baker immortalized R2-D2 with cement footprints of the droid outside Grauman's Chinese Theatre in Los Angeles.
Born in Birmingham, England, on August 24, 1934, Baker was 16 when he started performing with Burton Lester's Midgets, according to his website.
Baker also was a nightclub performer with the late British actor Jack Purvis, who appeared in "Star Wars: Episode IV - A New Hope," "Star Wars: Episode V - The Empire Strikes Back," and "Star Wars: Episode VI - Return of the Jedi."
Baker credited The Shaftesbury Society, a London Christian group that cares for children with disabilities, with helping him "overcome my height difficulties," according to his site.
He was married to actress Eileen Baker, who died in 1993. They had two children.