Am I just missing something here or is there not a way to retrieve a user's bio with the SE API? I looked at the documentation under the "Users" section, but I didn't find anything. Any suggestions?
By "bio" you mean the about me field, right? ...
For example, here is a query to get your "About me" on stackapps:
An easy way to create a filter is to use the filter-edit tool, on the appropriate doc page for the path you are using. :