It is a suit of armor that Peeves sometimes liked to hide in and scare people. They all participated in the Battle of Hogwarts after being animated via Piertotum Locomotor by Professor McGonagall. Unfortunately by the end of the battle all of the knights Professor McGonagall called had been destroyed.
It appeared officially in the set 4709 Hogwarts Castle of 2001, and 4842 Hogwarts Castle in 2010 and half of the knight appeared in 5378 Hogwarts Castle in 2007. In the 2010 castle, if the knight is rotated around it is seen that it is concealing Tom Riddle's Diary.
- In the Harry Potter Virtual Castle game, the knight is seen in its proper place in the set but then proceeds to appear in the library area whenever you visit it.