To find this information, you would need to:
* Know more about this specific William Showalter: Is he a famous person, a family member, or someone you know personally?
* Ask the person directly: If you know him, you could ask him what nicknames he uses.
* Search for information online: Try searching for "William Showalter nicknames" or "William Showalter aliases" in online databases or news articles.
Please provide more context so I can help you further.