Longcat is one of the first cat memes. It was discovered on 2chan days before the Lolcats. It is loved as an original meme and is one of the world's favourites. It is paired with the phrase "Longcat is Loooooooooooooooooooooooooooooooooooooooong". Unlike Lolcats, Longcat is it's own meme.
Longcat's real name is Shiroi (Shiroi is Japanese for white), and was originally posted on the internet by a Japanese man. Even though Shiroi is a female, she will almost always be referred to as a male.
Longccat is currently one of the most popular cat memes. Longcat also has an evil twin known as Tacgnol (Longcat backwards). Tacgnol is black and matches Longcat in length.
Long live Longcat.
Special thanks to Oh Internet for research purposes.