By Anthony McCartney
The Associated Press
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Danny Deraney, publicist for Kasem's daughter, Kerri, says Kasem died Sunday morning.
A statement issued by the family says he died at 3:23 a.m. on Father's Day morning surrounded by family and friends.
"Even though we know he is in a better place and no longer suffering, we are heartbroken," wrote his daughter Kerri Kasem on Twitter and Facebook from the family.
"The world will miss Casey Kasem, an incredible talent and humanitarian; we will miss our dad."
Kasem's "American Top 40" began on July 4, 1970, in Los Angeles.
The No. 1 song on his list then was "Mama Told Me Not to Come," by Three Dog Night.
The show continued in varying forms — and for varying syndicators — until his retirement in 2009.
In his signoff, he would tell viewers: "And don't forget: keep your feet on the ground and keep reaching for the stars."
Media personality Ryan Seacrest, who took over the countdown from Kasem in 2009, said in a statement that Kasem's death is a loss for radio listeners worldwide.
Seacrest said that as a child he'd listen to Kasem's show every weekend "and dream about someday becoming a radio DJ."
"When decades later I took over his AT40 countdown show, it was a surreal moment," Seacrest said.
"Casey had a distinctive friendly on-air voice, and he was just as affable and nice if you had the privilege to be in his company. He'll be greatly missed by all of us."
In recent years, Kasem was trapped in a feud between his three adult children and his second wife, former actress Jean Kasem.
In 2013, his children filed a legal petition to gain control of his health care, alleging that Kasem was suffering from advanced Parkinson's disease and that his wife was isolating him from friends and family members.
Kasem also suffered from Lewy Body Disease, a form of dementia.
A judge in May temporarily stripped his wife of her caretaker role after she moved him from a medical facility in Los Angeles to a friend's home in Washington.
Jean Kasem said she moved her husband to protect his privacy and to consult with doctors.
Casey Kasem developed a severe bedsore while in Washington and was in critical condition by the time he was hospitalized in early June.
It was a sad, startling end for a man whose voice had entertained and informed music lovers worldwide.
Kasem's "American Top 40" expanded to hundreds of stations, including Armed Forces Radio, and continued in varying forms — and for varying syndicators — into the 21st century.
He stepped down from "American Top 40" in 2004 and retired altogether in 2009, completing his musical journey with Shinedown's "Second Chance."
While many DJs convulsed their listeners with stunts and "morning zoo" snarkiness, Kasem would read "long distance dedications" of songs sent in by readers and introduce countdown records with sympathetic background anecdotes about the singers.
"The idea from the beginning was to do the type of thing on radio that Ed Sullivan did on television, good, honest stories with human interest," he told the Los Angeles Times in 1975.
Succeeding him at the main "American Top 40" show in 2004 was multiplatform star Ryan Seacrest, who has said he had been a fan of Kasem since boyhood and would imitate him in pretend countdown broadcasts at age 9.
Kasem's legacy reached well beyond music. His voice was heard in TV cartoons such as "Scooby-Doo" (he was Shaggy) and in numerous commercials.
"They are going to be playing Shaggy and Scooby-Doo for eons and eons," Kasem told The New York Times in 2004.
"And they're going to forget Casey Kasem — unless they happen to step on his star on the Hollywood Walk of Fame. I'll be one of those guys people say 'Who's that?' about.
And someone else will say, 'He's just some guy who used to be on the radio.'"
The son of Lebanese immigrants, Kasem was active in speaking out for greater understanding of Arab-Americans — both on political issues involving the Mideast and on arts and media issues.
"Arab-Americans are coming out of the closet," Kasem told The Associated Press in 1990.
"They are more outspoken now than ever before. People are beginning to realize who they really are, that they are not the people who yell and scream on their nightly newscast."
Kasem was born Kemal Amin Kasem in 1932 in Detroit.
He began his broadcasting career in the radio club at Detroit's Northwestern High School and was soon a disc jockey on WJBK radio in Detroit, initially calling himself Kemal Kasem.
In a 1997 visit with high school students in Dearborn, Mich., home to a large Arab-American community, he was asked why he changed his name to Casey.
"It didn't sound like a deejay; it wasn't hip. So we decided I'd be 'Casey at the Mike' — and I have been since," Kasem said.
In the 1975 Los Angeles Times interview, he said he had been doing "a regular screaming DJ show" in San Francisco in the early 1960s when his boss suggested he talk about the records instead.
He was unconvinced, since his screaming routine had brought him top ratings.
But he said he had learned "after a particularly unpleasant situation in Buffalo never to argue with general managers."