“Who came up with the Gregorian calendar—Greg or Ian?”

There have been several Gregorian (“Greg or Ian”) calendar jokes. “It may be somewhat difficult to believe, but the Gregorian calendar really was brought upon us by a guy named Greg and definitely NOT Ian” was posted on Twitter on April 26, 2010. “Happy Gregorian calendar day. Wherever you are, Greg or Ian, this one’s for you” was posted on Twitter on December 31, 2010. “Is it a Gregorian calendar? Well? Which is it? Greg or Ian?” was posted on Twitter on December 20, 2011.
 
A popular joke was posted on Twitter by Stu on May 20, 2018:
 
“Monday: Greg
Tuesday: Ian
Wednesday: Greg
Thursday: Ian
Friday: Greg
Gregorian Calendar.”
   
 
Wikipedia: Gregorian calendar
The Gregorian calendar is internationally the most widely used civil calendar. It is named after Pope Gregory XIII, who introduced it in October 1582.
   
Twitter
Pariah Carey
@jaseygalore
It may be somewhat difficult to believe, but the Gregorian calendar really was brought upon us by a guy named Greg and definitely NOT Ian.
4:57 AM - 26 Apr 2010
 
Twitter
~nick~nick~nick~nick~
@nickfourtimes
Happy Gregorian calendar day. Wherever you are, Greg or Ian, this one’s for you.
6:33 PM - 31 Dec 2010
 
Twitter
Stephen Rafferty
@srafferty73
Is it a Gregorian calendar? Well? Which is it? Greg or Ian?
7:27 AM - 30 Dec 2011
     
Twitter
Paraic O’Donnell
@paraicodonnell
The Gregorian calendar is so named because historians are uncertain whether it was devised by Pope Greg or Pope Ian.
2:38 PM - 31 Dec 2013
 
Twitter
Alan
@Meismorissette
Who came up with the Gregorian calendar Greg or Ian?
6:39 PM - 7 Jan 2014
 
Twitter
dan mentos
@DanMentos
FUN FACT: the gregorian calendar got its name when co-inventors greg and ian couldn’t agree on the name
12:13 AM - 2 Jan 2015
 
Twitter
Ollie
@ojedge
Father Time: “This ‘12 months’ business is great. Who came up with it?”
Greg: “Me”
Ian: “Me”
[invention of the Gregorian calendar]
6:02 AM - 31 May 2015
 
Twitter
Stu.
@dysondoc
Monday: Greg
Tuesday: Ian
Wednesday: Greg
Thursday: Ian
Friday: Greg
Gregorian Calendar.
2:52 AM - 20 May 2018
 
Reddit—Jokes
Monday: Greg Tuesday: Ian Wednesday: Greg Thursday: Ian Friday: Greg
submitted May 20, 2018 by peteypirate33
Gregorian Calendar.