I have always had a fascination with ninjas. As a kid I would spend endless hours doodling ninjas and reading my favourite comic GIJOE. Snake Eyes was my favourite.
The penguin ninja first appeared in Penguin Chat 3 early 2005. To unlock the ninja you would have to click the "n" in "penguin" to unlock the ninja. The secret penguin ninjas proved very popular.
The History of Club Penguin Ninjas
I had always planned to release ninjas before pets, pirates, and secret agents in Club Penguin. The original plan was to include the dojo in the Plaza, but the Pet Store and the Pizza Parlor were not ready, so the Dojo was hidden on the map with the iceberg. The mountain became the perfect home for the Dojo and later Card-jitsu. When Club Penguin launched on October 24th, 2005 the Dojo and all the clothing items were ready to be unlocked. (Including the sword) Then something happened.
The players wanted pets for their penguins!