Tuesday, Oct. 29, is National Cat Day, but it’s not just an occasion to watch cat videos.

According to the official website, National Cat Day was founded in 2005 to celebrate the love of cats as well as raise awareness about the number of cats that need to be rescued each year. Founder Colleen Paige of Animal Miracle Network hopes the nationally recognized day will shed light on the 4 million cats that are put in shelters each year and the 1 million to 2 million that are euthanized annually.

Paige said the goal of National Cat Day is to facilitate the adoption of 10,000 shelter cats nationwide every Oct. 29. The website provides links to suggested adoption agencies for those who are interested. Paige told the Examiner that nearly 1 million cats have been rescued since 2005.

However, not everyone can adopt a pet, so Paige suggests other ways to help, such as volunteering at a shelter, cat-sitting or even just spending some time with a friend’s feline.

Another way to celebrate is to read about the MasCAT Geoffrey, the mascot of National Cat Day. In 2012, an animal shelter volunteer found the stray cat in rough shape, with matted fur and a “red and raw” rear-end, likely from abuse. But Geoffrey’s tale has a happy ending: After being nursed back to health by the Animal Miracle Network, he was paired with his current owner, Anne Butler, a cat lover who suffers from severe degenerative arthritis. According to the Examiner, Geoffrey and Butler “are inseparable -- except when Geoffrey spots a loaf of bread (which he steals every chance he gets!)”

Geoffrey can only hope for the kind of fame enjoyed by fellow feline Tardar Sauce, nicknamed “Grumpy Cat,” who stole everyone’s hearts last year thanks to her forever grumpy expression. According to her owners, Bryan and Tabatha Bundesen, Tardar Sauce has a condition called feline dwarfism, which causes her to have “small sighs and stiff back legs,” ABC reported. But she's otherwise a really “healthy and happy cat,” says Bryan.

Grumpy Cat became famous thanks to social news-sharing website, Reddit, her owners said. "She was lying in my lap and she looked extremely grumpy, so I decided to put it on Reddit," Bryan told ABC News. "It went viral and I never expected it."

Grumpy, who now has a giant Internet fan base (close to 2 million likes on Facebook alone), has become an international celebrity, with myriad Internet memes and public appearances. Grumpy, who has starred in several commercials, will even make her film debut in the near future.

"It was an accident," Bryan told CNN of Grumpy’s fame. "We thought it would get some laughs, with the Internet liking cats. And it just kept going."

Other cats who've had their time in the limelight include Colonel Meow, Maru and Wasabi-Chan. Meet some of the most famous cats of the Internet below.

1.      Grumpy Cat

Despite her crabby disposition, Tardar Sauce, the famous “Grumpy Cat,” is actually really happy.

2.     Colonel Meow

Colonel Meow, a Himalayan-Persian cross-breed cat is not only a rising Internet star but was also awarded the Guinness World Record for longest fur, at nine inches.

3.     Sam, the cat with eyebrows

Sam, a cat with white perky ears and dramatic eyebrows like Groucho Marx, became famous thanks to the hashtag #CatsofInstagram.

4.     Geoffrey

Geoffrey, the MasCAT of National Cat Day, was a former stray cat who now lives happily with his new owner.

5.     Mushroom kitten

Wasabi-chan, who was rescued after being attacked by a crow, became famous after her Japanese owner uploaded photos of her in a crocheted mushroom costume.

6.     Business cat

This black cat with wide yellow eyes and a sharp suit emerged online back in 2011 and has been the subject of countless memes.

7.      Garfield

This tubby tabby was named the “world’s fattest cat” in 2012 by Guinness, but the world records organization stopped handing out that title out of concern that owners would begin to overfeed their cats to achieve a record.

8.     Lil Bub

Born the smallest in her litter, Lil Bub, a “perma-kitten” who is a dwarf and polydactyl cat, stole hearts with her kitten-like appearance.