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By 1954 Christiansen's son Godtfred Kirk Christiansen had become the junior managing director of the Lego Group. It was his conversation with an overseas buyer that struck the idea of a toy system. Godtfred saw the immense potential in Lego bricks to become a system for creative play but the bricks still had some problems from a technical standpoint: their locking ability was limited and they were not very versatile. In 1958 the modern brick design was developed but it took another five years to find the right material for it. The modern Lego brick was patented on January 28, 1958; bricks from that year are still compatible with current bricks.
Design
Lego pieces of all varieties are a part of a universal system. Despite variation in the design and purpose of individual pieces over the years, each remains compatible in some way with existing pieces. Lego bricks from 1958 still interlock with those made in 2010, and Lego sets for young children are compatible with those made for teenagers.