The story of the beloved Lego begins in Billund, Denmark, during the early 1930s. A master carpenter named Ole Kirk Kristiansen had established his business building stepladders, ironing boards, and stools, but with the onset of the Great Depression he had to shut the doors of his shop and let his employees go. To make money, he began creating wooden toys using leftover wood from his shop. The toys sold so well that he was able to hire back his employees under a new shop name: Leg Godt, or “play well” in Danish. At the time, Ole’s bestsellers were classic wooden pull toys with wheels that came in the shape of ducks or trucks.

Of Ole’s four sons, Godtfred took the most interest in the shop. He joined the family business at the age of 12, and father and son worked together to make their business successful. After World War II, Ole traveled to Copenhagen, where he saw a new invention: a plastic molding machine. The salesperson gave him a sample from the machine, which was a simple plastic brick from the British company Kiddicraft. Ole decided to add plastic toys to his workshop and began creating hollow plastic bricks similar to Kiddicraft’s bricks. They were sold in four colors, but they weren’t yet the Legos we know and love today.

It was Godtfred who moved the concept forward. He had noticed the frustration of users when their structures easily fell apart when moved—nothing was holding the bricks in place. So Godtfred pioneered and patented the now-standard Lego stud-and-tube configuration that gave the bricks “clutch power.” It was part of his new concept: the “Lego System in Play.” The idea of creating a system came to Godtfred during a trip to the London Toy Fair in 1954. While on the ferry crossing the North Sea, he had met up with a toy buyer. The buyer opined that instead of creating one-off products, toy makers should focus on developing a cohesive system in which sets of toys are interrelated. When Godtfred returned home, he laid out Lego’s “Principles of Play,” which were issued to every Lego employee: their toys would be limited in size without setting limitations on imagination; they would be affordable, simple, durable, offered in rich variations, made for both girls and boys at every age; and they would have no need of renewal and be easy to distribute.

Both the system and the stud-and-tube design were put into production in 1958, and the company hasn’t changed the design of its bricks since then: today’s Legos are compatible with every other Lego made from 1958 onward. (Side note: In April 1962, the Lego Group began producing miniature tires for adding wheels to Lego creations; in 2011, it became the largest tire manufacturing company of any kind in the world, when it made 381 million tires.)

In the first half of 2015, the Lego Group became the world’s largest toy company by revenue, with sales amounting to $2.1 billion. Today the company is still family owned, primarily by Godtfred’s son, Kjeld Kirk Kristiansen.