The following is a list of background characters. As the title suggests, these characters have primarily been used in scenes where numerous characters were needed (such as large crowds), and, as a result, are also recurring characters. However, these kinds of characters typically remain unnamed due to never playing any significant role throughout the series. Among storyboard artists and animators, such characters are usually identified by model numbers and referred to as incidentals to tell them apart.
Luckily, some of these characters were named in both production artwork and episode end title credits, so they're easier to identify.