Lennon got the idea for this song from a newspaper article he read about a miser who hid his cash everywhere so nobody could find it. The article appeared in the Daily Mirror
on June 7, 1967, with the headline, "Scotsman's Meanness 'Was Cruel.'"
"Mr. Mustard" was John Mustard, who was described in the story as "an exceptionally mean man." His wife was divorcing him because, among other things, she couldn't stand being in the dark all the time - he insisted on keeping the lights off most of the time to save money.
It wasn't the first time John Lennon was inspired by a newspaper story: some of the lyrics in "A Day In The Life
" came from articles he read in the Daily Mail