Tacgnol is a popular internet meme. He is a black cat, the counterpart and main enemy of Longcat (Tacgnol = Longcat in reverse order).
The myth of Longcat originated from the picture of a white cat being held in the air by his armpits, thus making him look very long. It soon became the source of many funny pictures which emphasized Longcat's extreme length and power. As he was thought to represent the forces of good, people started considering a nemesis for him, then Tacgnol was born.
Tacgnol is similar to Longcat, only he is black and evil. It has been said that one day they're going to clash in an apocalyptic battle known as the Catnarok.