The cute little girl, the youngest of the bunch, at times annoyed and endeared the audience.   Some of the most popular episodes involved Monica, and after her introduction, she became the subject of more fan fiction than any other character (much of which can still be read in the usenet newsgroup alt.fan.lilbill).

Interesting facts about Messy Monica:

• Monica was originally going to be called "Baby Mon'ca" and was envisioned as a much younger character, barely a toddler.  But in early concept sketches, her big eyes, blue dress, and pacifier [insert oral-fixation joke here] made her too remeniscent of Maggie Simpson.
  
  
• Over the course of the three seasons in which Monica appeared, some of the stains on her dress have been caused by: grape juice, gravy, skunk, ice cream, grass, candle wax, glue, ketchup, shoe polish, lipstick, grease oil, and something left behind by Socks the Flying Cat during a moment not caught on camera.
  
  
• In the closing credits of each episode during the last three seasons, there is a credit for "Monica's Slippers Designed By" and that credit is given to a different person each episode.  Those people are all friends or family members of writers on the show.