When was the first king size bed made?
No context provided
When was the first larger mattresses that were later standardized as king size beds made?
mid-1940s
No context provided
When was the first standardized king size bed made?
1950s
Kingsize
https://en.wikipedia.org/wiki/Kingsize
Historically most beds were "twins" or "doubles" but in the mid–1940s larger mattresses were introduced by manufacturers.
Bed size
Larger mattresses that were later standardized as king size beds were made in the mid-1940s. Before then, most beds had been either twins or doubles. The first standardized king size beds were made in the 1950s. 