Suppose your co-author on a project wants to be identified by an online pseudonym such as "Funkmaster A" instead of his or her real name. (I didn't make up that handle as a purely hypothetical example, by the way. Someone I know went by that, once upon a time.)
William Sealy Gosset in 1908 (age 32). Source: Wikimedia Commons Pseudonyms can be necessary. William Sealy Gosset was only permitted to publish under the pseudonym Student while he worked at the Guiness brewery, and thus we have Student's t-test rather than Gosset's t-test. Sometimes a person's survival may depend on the use of an alias. Anonymity offers protection. Pseudonyms affect apparent credibility. "Funkmaster A" does not immediately strike people as the name of a psychologist instructor who has written six published books, but he is (under his real name, though). Listed with other, "normal" names, its use can seem like attention-seeking behavior even if it had been perfectly appropriate for the original circumstances in which it was used. For the very reason that anonymity offers protection, it also diminishes accountability.
When creating a pseudonym for publication purposes, an individual has the freedom to devise something that will optimally suit the process. For example, a person might go by Aaron Aardvark for optimal placement in alphabetical order, regardless of whether a particular list organizes by first or last name.
Aardvark, A. (2018)....
A pseudonym such as Funkmaster A raises another problem, though, one that I have had to deal with on my own CV. I was on a convention panel which included a panelist who also went by a pseudonym that consisted of one word followed by the letter K, and I'm still not sure if I chose the right way to list her in that citation on my CV. How do you cite someone like Funkmaster A in a publication? Reporting that Smith, A, & Wesson (2018) made a discovery looks like an error or like A. is the first initial when you're trying to distinguish multiple Smiths within the same article. Imagine what it looks like in the reference section.
Smith, J. J., A., F., & Wesson, O. (2018)....
This issue isn't just about pseudonyms, though. There are people in the world who have single-letter surnames, and made of them readily report the hassles they have to face over them. Computers do not handle them well - for example, rejecting credit card applications because their systems are programmed to process no names shorter than two letters long. So how do we cite one-letter surnames in APA style? Frankly, I have not yet found a definitive answer.
THE BASICS