He may not have had a seat in the Senate, but Splash Kennedy left an everlasting impression in the chambers of Congress and even at the White House.
"At Teddy's side, Splash became a world-class fetcher of tennis balls and a meeter and greeter of presidents, senators, congressmen and even foreign dignitaries," Kennedy's widow, Vicki, said in an e-mail announcing his death.
Splash and the Kennedy's other dogs, Sunny and Cappy, were a constant fixture at the late senator's side.
Whether he was voting on important pieces of legislation or meeting with guests and dignitaries or the president of the United States, it wasn't unusual to see Kennedy with at least one of his dogs.
The longtime senator's love for his Portuguese water dogs even inspired President Obama, who promised his daughters a puppy if he won the campaign. The first family's dog, Bo, was a gift from Kennedy and was bred by the same breeders as his own three dogs.
"I am proud to endorse the Portuguese Water dog as the next First Dog (or Dogs) of the United States," Kennedy said in a statement last year when the Obamas were hunting for the first pet. "They have a can do and hopeful spirit, they are smart, they are resilient, they are determined, they are optimistic, and they are tireless."
"They're loyal, smart, loving and they become a real part of the family. And they definitely do not shed," he added.
Perhaps what Splash will be remembered for the most is being the narrator in a children's book -- penned by his owner -- titled "My Senator and Me: A Dog's Eye View Of Washington, D.C."
The book was published in 2006 and is designed to teach children about the political process.
After all, Splash was an important member of Congress, having presided in influential meetings and many a hearing.
Splash Kennedy Dies at 13
On sunny summer days, Kennedy would often be spotted playing with tennis balls with his dogs on Capitol Hill, even carrying dog poop bags to clean up after his pets.
"I take Sunny and Splash to the Senate with me, and they love being around people and being part of the action," Kennedy said in a statement endorsing a Portuguese water dog for the first family. "In fact, they're so much fun that we've just added a new Portuguese water dog puppy to our family -- Captains Courageous is his name. We call him Cappy for short. And he's another winner."
The curly-haired pets also gained celebrity status in Kennedy's hometown of Hyannis Port, Mass. Kennedy would often take strolls along the dock at the Hyannis Port Yacht Club and sail with his two pets on his beloved 50-foot wooden schooner, Mya.
"Sailing on Mya with Vicki at my side and my dogs, Splash and Sunny, at my feet. And, of course, a Democrat in the White House and regaining our majority in the Senate," Kennedy said in a Vanity Fair interview in 2006, when asked about his idea of perfect happiness.
ABC News' Andrea Dorning and The Associated Press contributed to this report.