In the thread at the end of the post the asker asks for pseudonyms for famous mathematicians or (secretive) groups of famous mathematicians. The famous "Bourbaki book series" is an example of a book series published by a group of people under a "pseudonym". Are there other similar examples of "book series" published under a pseudonym, where famous mathematicians write a series of papers and publish them like this?
https://mathoverflow.net/questions/45185/pseudonyms-of-famous-mathematicians
"As of 2000, Bourbaki has had "about forty" members. Historically the group has numbered about ten to twelve members at any given point, although it was briefly (and officially) limited to nine members at the time of founding. Bourbaki's membership has been described in terms of generations:
$$ \text{ }$$ .... After the first three generations there were roughly twenty later members, not including current participants. Bourbaki has a custom of keeping its current membership secret, a practice meant to ensure that its output is presented as a collective, unified effort under the Bourbaki pseudonym, not attributable to any one author (e.g. for purposes of copyright or royalty payment). This secrecy is also intended to deter unwanted attention which could disrupt normal operations. However, former members freely discuss Bourbaki's internal practices upon departure."
https://en.wikipedia.org/wiki/Nicolas_Bourbaki#Membership
There is moreover the "John Rainwater" pseudonym: "The fictitious mathematician John Rainwater was created as a student prank but has become known as the author of important results in functional analysis. At the University of Washington in 1952, John Rainwater was invented and enrolled in a mathematics course by graduate students who were in possession of a duplicate student-registration form. Later, mathematicians published under the pseudonym of John Rainwater. Papers were published under the name Rainwater mainly in functional analysis, particularly in the geometric theory of Banach spaces and in convex functions. Rainwater's theorem is an important result in summability theory and functional analysis. The University of Washington's seminar in functional analysis is called the Rainwater seminar, and the associated Rainwater notes have influenced Banach-space theory and convex analysis."
Question 1: Have similar pseudonyms existed in other fields - fields such as algebra, algebraic geometry, topology, representation theory? What is the "most distinguished" result first published by a "pseudonym"?
https://en.wikipedia.org/wiki/John_Rainwater
There is a twitter page for fictious "Betty Bourbaki" - a fictious person created by the Bourbaki group:
"The group developed some variants of the word "Bourbaki" for internal use. The noun "Bourbaki" might refer to the group proper or to an individual member, e.g. "André Weil was a Bourbaki." "Bourbakist" is sometimes used to refer to members but also denotes associates, supporters, and enthusiasts. To "bourbakize" meant to take a poor existing text and to improve it through an editing process. Bourbaki's culture of humor has been described as an important factor in the group's social cohesion and capacity to survive, smoothing over tensions of heated debate. As of 2021, a Twitter account registered to "Betty_Bourbaki" provides regular updates on the group's activity."
https://twitter.com/betty_bourbaki
Question 2: Has the Bourbaki group created other "fictious persons", other than Betty Bourbaki? The twitter "Betty Bourbaki" page seems real and keeps announcing Bourbaki seminars in math in Paris - There is no mentioning that it is in fact "fake news". If someone (someone living in an area without proper net-connetion, like Kashmir or any other similar place) visiting the Betty Bourbaki site did not have access to wikipedia, this person would not understand that Nicholas Bourbaki and Betty Bourbaki are fake.
Another example would be D.H.J. Polymath, author of several papers coming from "polymath projects", collaborative efforts of dozens of mathematicians and started by Tim Gowers in 2009. In particular Polymath 8 made a great deal of progress toward the Twin Primes Conjecture, although the conjecture itself is still out of reach.