Apologies if the answer is elsewhere but I put in some time looking and can't find it.
I have bbpress integrated with WordPress, and on the WordPress end of things, when people who have registered with bbpress login to WordPress, their username displays on comments as "Anonymous." (I have disabled anonymous commenting, but this is a separate issue.)
I went into this user's account and the Nickname and Display Name fields were blank. Changing the display name to the person's username fixed this. But I don't want to have to do this for every user who registers via bbpress.