Emmanuel "Manny" Heffley is the younger brother of Rodrick and Greg Heffley who is constantly pampered and spoiled by his parents. As the youngest child of the Heffley family, he plays a major role in Diary of a Wimpy Kid series, having appeared in all the main series books to date.

Given estimates made based on illustrations of him, Manny Heffley is most likely between 1' 3" (38.1 cm) and 1' 4" (40.64 cm) tall, which would make him shorter than the average newborn baby. However, this is entirely conjecture, as his height has never been stated definitively within the series.