- --Manny Heffley, said as an abusive word to Greg
- --Manny Heffley, the way Manny says brother
Manuel "Manny" Heffley is Greg and Rodrick's younger brother, and is a minor antagonist in most of the series as well as a major antagonist for the second half. In the movie, he is played by twins Connor and Owen Fielding. Manny is loosely based on Pat Kinney, Jeff Kinney's younger brother.[confirmation needed]
Manny Heffley is thought of by Greg to be evil and overly spoiled by his parents. Greg believes that his parents treat Manny like a prince; he always gets out of trouble, and gets whatever he wants by appearing cute, troubled or crying. This always makes Greg unhappy because he, nor his brother Rodrick, had ever gotten as many privileges as Manny, when they were his age. Manny can't seem to get the concept of potty training; this is mainly because of Uncle Joe (Greg in the film) telling him to watch out for the Potty Monster, which had prevented him from ever stepping into the bathroom for six months. According to the first book, Manny is a fan of the television show ZOOM, especially the Family Couch ZOOM Playhouse. He also watches a show called "The Snurples", which according to a newspaper sets kids back in social skills and language development (Manny starts speaking gibberish). Manny has shown that this is true - he has no real friends and never plays with other kids in playgroups, but has imaginary ones and uses these to get out of trouble and get extra food. Despite his seemingly air-headed exterior, Manny has shown that he can be very cunning, deceitful, manipulative, and intelligent for his age in unexpected ways. When Susan let him play on Greg's Net Kritterz account, he figured out how to sell all of his brother's items and change his password. He has also locked out the entire family from watching any TV shows except for his personal favorite cartoons. He also has been shown to speak Spanish, in The Long Haul.
Manny has also been characterized as extremely uncaring and holds powerful grudges that has endangered the family on multiple occasions. One of these is shown in Cabin Fever, where he shuts off all the lights as well as the air conditioning to every room except his own just because he wasn't taught how to tie his shoes. This caused the entire family to suffer in cold weather and starvation until Greg finally discovered the scandal.
Manny's unusual personality can however significantly help the Heffley family as a whole. Manny can speak Spanish properly, and that's just from listening to hours of Spanish-English wordbook-CDs that his mother bought from a local store. He also has an extreme ability of learning new things and abilities, which again, is shown when he learns to speak proper Spanish after just a few hours.
The fact Manny is able to learn perfect Spanish, change Greg's password, the parental lock, and kill all the lights except for his room is quite surprising for a child his age, meaning he is quite intelligent but is still socially awkward.
It is likely that Manny knows about his parents' favoritism towards him, and he takes advantage of this. This includes breaking Greg's gaming console, drawing on his bedroom door, taking a dirty magazine to day care, and twisting the "No Swearing" rule in such a way that he makes money out of it.
- Greg's illustrations depict Manny having an overbite and his teeth being spaced far apart. He looks like "a bucktoothed alligator", according to the movie diary. Manny is always depicted with a white shirt and black shorts. Much like Greg, he has protruded hair, with three lines sticking out. Manny is about the size of a letter in Greg's journal.
- Manny appears to be less spoiled in Cabin Fever then he is in other books.
- Manny is known to break, spoil or sell Greg's things.
- Susan Heffley (Their mom) made something called No Pants After Dinner, also stating that he needs potty training.
- He is one of the smallest characters in the Wimpy Kid series as he is only smaller than his father's and his mother's head.
- In the first book, after he yells "Bubby" at Greg on the stage, Greg says he's been able to keep that nickname quiet for 5 years, meaning Manny must be at least 6, but his size and behaviour contradict him from being 6. There is another contradiction in Rodrick Rules, where it says that he was 3, and again in The Last Straw, where it says Manny has been held back from preschool three or four times. However, it is also possible that Greg used the five years thing as an expression.
- In the online version, Manny is allergic to peaches. Greg also mentions this in The Ugly Truth.
- Manny is favoured by Susan Heffley and Gramma.
- The only members of the family who do not appear to like him are Aunt Cakey, Greg Heffley and Rodrick Heffley.
- Manny serves as one of the main antagonists in Cabin Fever.
- Manny is quite smart, as he knew how to change the password to both, Greg's Net Kritterz account, so Greg can't log back in, the TV parental locks so he can watch whatever he likes, and also learned Spanish and the Snurple language fluently relatively fast.
- Manny loves Bitter Apple Spray, so he probably likes sour and bitter food.
- Manny also gives Greg two nicknames: Bubby (affectionate) and Ploopy (derogatory)
- According, to the first book, Manny started calling Greg Bubby since he couldn't pronounce "Brother",
- Greg states that Manny is a tattletale and had telling on him since he could talk. He also told his parents what wrong deeds Greg did before he could talk.
- He is fluent in Spanish.
- The main reason the producers picked twins was because they felt that twins would be easier to work with (on account that there would a backup should one refuse to cooperate.
- He makes a lot of money because he gets paid for the older Heffleys' swearing, using the potty, and selling his own drawings. Therefore, Greg describes him as "rich".
- He can't pronounce his "R"s, and Greg couldn't when he was preschool age either.
- Aunt Cakey seems immune to his whole act.
- He may be modeled after Igdoof's little brother