Ninja was a theme and product range of the construction toy Lego. Launched in 1998, the collection was its own theme. It had many elements of the ninja warriors from feudal Japan. The majority of the sets were released in 1998 and 1999, with only three small sets of minifigures released in 2000 as part of the ‘Mini Heroes Collection’. After this, the theme was discontinued, and was effectively replaced by the “Knights Castle” theme from 2000 on-wards.
In 2011 Lego decided to release a new line called Lego Ninjago Masters of Spinjitzu, which uses elements from the previous Ninja series.