Lil Bub and Grumpy Cat claw their way into bookstores

Two tiny cats, two big YouTube/Internet sensations, and now two awww-inspiring books. Lil Bub's Lil Book (Gotham, on sale Tuesday) and Grumpy Cat: A Grumpy Book (Chronicle, in stores) are filled with photos of the famed pusses and lots of certitude.

Who are these guys? Well, first, they're both girls.

A few facts:

Grumpy Cat:

Real name: Tardar Sauce

How she got her nickname: Specializes in frowny faces

Age: 1

Other stats: Has feline dwarfism; weighs under 5 pounds

Her human: Tabatha Bundesen

Accolades: 2013 Webby Award for Meme of the Year

Social media: 1 million+ Facebook likes; 100,000+ Twitter followers

Lil Bub:

Nickname: Bub

Family background: Born the runt of a feral litter

Age: 2

Why her tongue sticks out: Born with genetic mutations including underdeveloped lower jaw and no teeth

Weighs: 4 pounds

Her human: Mike Bridavsky

Film credits: Stars in Lil Bub & Friendz