Uga was the winningest mascot in the university's history - the football team was 87-27 and won two SEC titles in his tenure.
At 65 pounds, he was also the biggest of the mascots, more than 20 pounds heavier than his father.
"His heart just played out. He suffered no pain and died peacefully," Seiler said in a news release from the university.
Uga, who would have turned 10 on July 22, became the mascot during an emotional pregame ceremony before the 1999 Georgia-South Carolina game. At that time he took over for his father, Uga V, who Sports Illustrated had named college football's best mascot.
He'll be buried in a marble vault in the southwest corner of Sanford Stadium in the same area where the other Ugas are entombed. The ceremony, which the university says will be private, will be held early next week, possibly as early as Monday.
"He was a good one," Seiler said. "What can I say? He had a marvelous record. He was a very strong and healthy dog. He was the biggest of all the dogs, and he had the biggest heart. It just played out."
The Seilers had hoped Uga VI would be able to take the field this fall when the football team begins a season which many believe may end in a bid for a national championship. But Seiler said he noticed Uga breathing heavily when he arrived home from work Friday. He was taken to the family veterinarian in Savannah, who consulted with the university's College of Veterinary Medicine.
A successor to Uga VI will be named at a later date, but Seiler said the lineage is secure and that Uga VII is waiting in the wings.
"This is a very sad day for the entire Bulldog Nation," said Damon Evans, Georgia's athletic director and a Gainesville native. "Uga has always been such a strong figure associated with the University of Georgia nationwide. Uga VI was a damn good mascot and a damn good dog. He was an outstanding representative of our fine institution. While this is a sad day for all Bulldog fans, our condolences especially go out to the Seiler family."
Trey Paris, president of the UGA Alumni Association and a Gainesville resident, extended his condolences to the Seiler family.
"UGA VI was indeed a damn good dog," Paris said. "Alumni of all ages had a special relationship with him, and he always drew a crowd of alumni faithful, whether at the Sugar Bowl, the Homecoming Parade, or simply walking into Sanford Stadium before leading us to victory. We will miss him and all he stood for."
Gov. Sonny Perdue said in a statement that Uga was a tremendous ambassador not only for the university, but also the state. Perdue said Uga made an appearance a few weeks ago at an economic development conference held in Savannah with officials from Canadian provinces and neighboring Southeastern states.
"Though much of the Bulldogs' success in recent years has been attributed to Coach Mark Richt, most true Georgia fans know that his job will be much tougher now without the winningest Uga of all time stalking the sidelines, sitting on his trademark bag of ice and carefully eyeing any opposing mascot that dared to come close," Perdue said.
The Seiler family has owned all of the Ugas. The first Uga was a wedding present to Sonny and Cecelia Seiler from a friend in Columbus. Later, they began taking the dog to the football games, and then-coach Wally Butts suggested that the Seilers make their dog the university's official mascot.
Since then, the all-white English bulldogs have become one of the University of Georgia's most famous symbols and, arguably, one of the most famous icons in all of college football.
Uga III presided over SEC titles in 1976 and 1980, and he was present in New Orleans when Georgia won the national championship on Jan. 1, 1981.
Uga IV, wearing a tuxedo, accompanied Herschel Walker to New York to accept the Heisman Trophy at the end of the 1982 season.
Uga V became famous for lunging at an Auburn wide receiver who got too close to him on the sidelines after catching a touchdown pass in 1996.
In addition to being named the nation's top mascot by Sports Illustrated, Uga V also co-starred in the movie "Midnight in the Garden of Good and Evil."
The tenure of Uga VI was arguably the university's most successful athletically.
The football team had an 87-27 record during Uga VI's reign as mascot, won both the 2002 and 2005 SEC Championships and won six of eight bowl games over that span. Uga VI's record surpassed the mark of 77-24-4 achieved during Uga IV's stint as mascot.
And it wasn't just football that saw success.
Nineteen of UGA's 35 national championships have been won in Uga VI's tenure, including this year's gymnastics, men's tennis and equestrian titles. Georgia teams have also was 35 SEC titles under Uga VI.
Georgia has also had six top-10 finishes in the Director's Cup, the annual all-sports competition among the nation's top athletic programs.
Uga VI's registered name was "Uga V's Whatchagot Loran?" - a reference to the famous question legendary announcer Larry Munson asks of sideline reporter Loran Smith.