The LEGO theme launched in 1978 around knights, castles, and medieval kingdoms was LEGO Castle.
LEGO Castle was one of three major product themes introduced in 1978, alongside LEGO Space and LEGO Town. Its early sets established the classic LEGO medieval world with fortress walls, drawbridges, mounted knights, horses, shields, and heraldic symbols.
The theme developed through many subthemes and factions. Notable groups included the Black Falcons, Crusaders, Black Knights, Forestmen, Wolfpack, and the fantasy-oriented Fright Knights. These factions helped LEGO create stories and rivalries without requiring a single continuous storyline.
LEGO Castle is sometimes confused with LEGO Kingdoms, a later medieval-themed line, or LEGO Vikings, which focused on Norse-inspired warriors and ships. Castle is the broader and original LEGO medieval theme, beginning in 1978 and returning in several forms over the decades.