The cat's unusual appearance was not in fact due to her temperament but an unusual combination of an underbite and feline dwarfism, a form of genetic mutation.
Bundesen always maintained that Grumpy was in fact very pleasant and playful.
Such was Grumpy Cat's fame that her owners began a full-time publicity operation to fulfill demand for personal appearances.
She appeared at the SXSW festival and on several commercials.
The official Grumpy Cat shop lists 883 items for sale, including books, T-shirts, calendars and temporary tattoos.
And in 2013, the Bundesens launched Grumppucino, a branded coffee drink.