From PEOPLE Magazine Click to enlarge
Cesar Millan may be the country's most famous pack leader, but he's quick to admit he acquired much of his canine wisdom from his right-hand dog, Daddy. "He's my sensei. He totally showed me what mastering acceptance looks like," Millan, 40, told PEOPLE in September, already dreading the day he'd have to say goodbye to his aging pit bull. "I'm gonna miss him."

On Feb. 19 the Dog Whisperer's beloved pet and costar died, "peacefully and surrounded by family," at 16. Daddy, who had successfully battled cancer last year, "brought my family and me so much joy," Millan said in a statement. "He represented what my grandfather taught me: Never work against Mother Nature."

Daddy had been a member of Millan's family since his original owner, rap artist Redman, gave the 4-month-old pup to the then-unknown dog trainer. As Millan went on to star in the hit National Geographic Channel series and write four bestsellers, he used Daddy—and his unflappable calm-submissive energy—as a training tool and example of how even breeds with tough reputations can be model pets. "Everywhere he goes he spreads peace. A cat, a rabbit, people who don't like pit bulls . . . Daddy accepts them all," says Millan. "His existence has touched a lot of people."