“John Dough” is a baker pun on “John Doe” (an name for an unidentified man). “The secretive baker died last week. His name was John Dough” was posted on Twitter  on May 11, 2011. “The anonymous baker, John Dough” was posted on Twitter on October 26, 2011.
 
A riddle was posted on Reddit—Jokes on August 9, 2017:
 
Q: What do you call an unknown baker?
A: John Dough.
 
     
Wikipedia: John Doe
“John Doe”, “John Roe” or “Richard Roe” (for men), “Jane Doe” or “Jane Roe” (for women), and “Baby Doe”, “Janie Doe” or “Johnny Doe” (for children), or just “Doe” or “Roe” are multiple-use names that have two distinct usages. Firstly, and especially in the United States, Canada and Ireland, they may refer to an unidentified person, or a party in a legal action whose identity is being withheld officially. In the context of law enforcement in the United States, such names are often used to refer to a corpse whose identity is unknown or unconfirmed. Secondly, such names are also often used to refer to a hypothetical “everyman” in other contexts, in a manner similar to “John Q. Public” or “Joe Public”.
     
Google Groups: alt.humor.puns
farmer
nemo
4/19/04
(...)
Or was it to the well-known correctly spelled baker, John Dough?
     
Twitter 
Bernadette Woodlands
@Ber_TheWoods
The secretive baker died last week. His name was John Dough
7:09 AM - 11 May 2011
   
Twitter
Nikes
@AlexLeeDee
The anonymous baker, John Dough
6:27 PM - 26 Oct 2011
   
Twitter
Sounds Locke!
@SoundsLocke
John Dough, the anonymous baker.
1:33 PM - 9 Dec 2011
   
Twitter
Gareth E. Rees
@hackneymarshman
Question of the day: When an unidentified baker is found dead, do the police refer to him as a John Dough?
7:16 AM - 17 Jan 2012
   
Twitter
TOMMIxᵀᴼᴹᴹᴵˣ
@tommixhelsinki
If an uidentified baker turns upp dead. Will they call him John Dough?
7:11 AM - 20 May 2013
   
Twitter
Steven Oblander
@StevenOblander
John Doe is an anonymous person. John Dough is an anonymous baker.
3:20 PM - 19 Mar 2014
 
Twitter
Davey Six-Toes
@HutchinsonDave
My favourite anonymous baker is John Dough.
7:38 PM - 30 Mar 2015
   
Twitter
Gabby 🔮
@ArkGev363
What do you call a baker with no identity?
John Dough.
11:59 PM - 19 Feb 2017
 
Reddit—Jokes
What do you call an unknown baker?
submitted August 9, 2017 by essenceofpotato
John Dough
 
Twitter
Ronny Pascale
@ronnypascale
My local baker won’t tell me his name. I call him John Dough.
1:03 PM - 18 Mar 2018
     
Reddit—Jokes
What do you call a baker who has no identity?
submitted May 18, 2018 by TempMage
John Dough
 
Reddit—Dad Jokes
What was the unknown baker’s name? (self.dadjokes)
submitted June 14, 2018 by virgindroy
John Dough.