In 1968, Charlotte Rude and Hjördis Olsson-Une were two young graduates of Sweden's Konstfack University, where they had studied art and design. The two moved to Älmhult, Sweden, where a glassworks was located; having caught the material exploration bug at design school, the two wanted to experiment with glass.

The pair had very little money and shared an apartment. To furnish it, they bought inexpensive leftover particle board from a nearby construction site, and built pieces they designed themselves.

Älmhult was also where Ikea had opened their first store, back in 1958, and was where their headquarters were based. Some of Rude and Olsson-Une's neighbors worked for Ikea, and when they saw the designers' self-created furniture, encouraged them to try to sell the designs to Ikea. The neighbors introduced them to Ikea manager Gillis Lundgren.

Lundgren didn't buy their designs. Instead he offered them full-time jobs. The duo accepted, and soon began designing furniture.

In 1970s, the Ikea store in Stockholm suffered a fire and needed to be rebuilt. The brass decided they may as well add a large play area for children. The task of designing the play area fell to Rude and Olsson-Une, who were then Ikea's youngest designers. The two designed a sort of indoor playground filled with pillows, ropes and platforms.

But "the biggest star of the play area," according to Ikea, "was the ball pit."

The idea came when Charlotte and Hjördis were opening boxes containing a new type of protective packing material. It consisted of small plastic balls, and reminded Charlotte of the then wildly popular bean bags that kids would sit and lie down in.

They imagined how one could jump and swim around in a sea of balls if it was deep and wide enough. However, these balls were too small. Children might put them in their mouths and choke. At the time, plastic was growing fast as a material, and the young designers soon found lighter and bigger multicoloured balls to use.

A huge wooden box – deep enough to jump into – was built with particleboard and filled with thousands of balls. When the play area opened in 1971, the ball pit became a huge hit. Kids loved it, and families were soon rushing to IKEA to let their children try out the new invention. Later in the 1970s, ball pits of all sorts started popping up in everything from amusement parks to fast-food restaurants, but the ball pit in the Stockholm IKEA store in 1971 was likely the first one in the world.

Rude and Olsson-Une didn't stay at Ikea for long; after just five years, in 1973, they moved to Copenhagen to pursue graduate studies at the Royal Danish Academy of Fine Arts. They took on freelance design work--and apparently faded into obscurity. I can find no record of their work after their time at Ikea.