Whats The K in K-mart?

Answer 1

The K is from the founder's surname - Kresge.

More than one hundred years ago, Sebastian Spering Kresge opened a modest five-and-dime store in downtown Detroit...and changed the entire landscape of retailing.
By the mid-1920s, the S.S. Kresge Company was opening locations that sold items for $1 or less, a precursor to the current discount store.
In 1977, nearly 95 percent of S.S. Kresge Company sales were generated by Kmart stores. To reflect this dramatic impact, the company officially changed its name to Kmart Corporation.

The history is found at the link below.