100 years ago this week Gene Ahern, in his Our Boarding House panel, started a sequence that would have a great impact. In 1922 the week began on the Monday of January 23 and featured a mystery stretching through the week. (Click on panels to embiggen, a second click will supersize.)
January 23, 1922: 
January 24, 1922: 
January 25, 1922: 
January 26, 1922: 
Then on January 27, 1922, true to Martha’s word, the guest appeared.
And the world was introduced to Martha’s errant husband Major Amos B. Hoople!
By the next day Clyde, Buster, and Mack had become aware of Amos’ Munchausenistic tendencies.
The following Monday (January 30) saw the Major delighting
Miss Church and Mrs. Hoople with his fantastical tales.
But Our Boarding House would remain very much an ensemble comic for over a year after the introduction of The Major. Those already mentioned plus Miss Herzog and Alvin would share the spotlight. Amos Hoople would take a more or less weekly turn as the featured personality.
February 2, 1922: 
February 11, 1922: 
February 16, 1922: 
By 1923 Major Amos. B. Hoople had gained stature physically and in popularity.
And it wouldn’t be long before Major Hoople was the undisputed star.
Eventually his name would have marquee value.
June 19, 1936: 
postscript: The Fez Years (see Hart Liss’ comment below)
Our Boarding House panels dated October 15, 1928 and December 3, 1928
Ah, but the first question after when did he first appear is when did he start wearing a fez?
That was rather heartless of you Hart, but I did some digging.
No guarantees, since I didn’t read every OBH panel between 1922 and 1928, but the first first panel I found with the fez was on October 15, 1928 as The Major is dressed to retire for the evening. Then the more recognizable white fez shows itself for two weeks straight during a doctor ordered orange juice fast running December 3 to December 16, 1928.
(samples have been added to the above article)
note: This is for the dailies, I didn’t check the Sunday pages.