Mould King is a brand known for producing building block sets that are compatible with other major brands of building blocks, like LEGO. They offer a wide range of products, from architectural models and vehicles to fantasy and complex technical sets. Mould King sets are often appreciated for their quality and detailed designs, providing options for both children and adult enthusiasts. They sometimes focus on creating large, intricate models that can be appealing to advanced builders looking for a challenge. The brand is one of many in a growing market of alternative building block manufacturers, known for offering more affordable options compared to some mainstream brands.