The youngest Williams sister has two dogs, a Jack Russell terrier named Jackie and a Maltese named Lorelei. Serena has had Jackie since she was in high school and named her after Mariah Carey's Jack Russell Jack.
"I take my Jack Russell everywhere," Williams told PEOPLE. "I am so busy with tennis and my business interests, but I wanted to be at the game to support the team, and Jackie likes to be part of everything I do."
Poodle Pierre might be more well known than his World No. 1-ranked dad. The pup has his own Twitter page and has posed with Djokovic for the cover of L'Uomo Vogue. Whether they're sharing a meal or vacationing together, this pair is inseparable.
Venus has three dogs: two Cavalier King Charles spaniels and a Havanese named Harold. "You're out there on your own and you need a friend who's there for you – wins, losses – and who really cares for you," she said last year in a U.S. Open promo clip. "I've recently found that someone, and that's Harold." The pup frequently travels with Venus and knows his Aunt Serena and her dogs very well.
In 2007, Sharapova starred in a series of Canon PowerShot TV spots featuring a caramel-coated Pomeranian named Dolce. While the dog in the commercials was an actor dog named Beowulf, Sharapova really does own a Pomeranian named Dolce – and she really does take "tons of photos" of her little guy.
Courtesy Andy Roddick; Inset: Jay West / WireImage
Roddick, who turned 29 today, named his English bulldog Billie Jean after the tennis legend Billie Jean King. He shares the pup with his supermodel wife, Brooklyn Decker. The couple spends a great deal of quality time with Billie, but sometimes it just isn't possible. "You know, we've had to keep up her self-esteem, because the airlines have deemed her too fat to fit on a plane," Roddick told ESPN. "So we have to constantly shower her with love and build up that self-esteem and tell her she's beautiful." Aww!