Cast[]
- Thomas as Greg Heffley (both main characters, smart, kind and positive and left out at times)
- Percy as Rowley Jefferson (both cool, nice and best pals to Thomas and Greg)
- James as Rodrick Heffley (both vain, strict and think they know everything)
- Bill/Ben as Manny Heffley
- Gordon as Frank Heffley (both cocky at times and father figures to Thomas and Greg)
- Molly as Susan Heffley (both love Gordon and Frank)
- Peter Sam as Lil' Cutie
- Mavis as Heather Hills (both stubborn at first)
- Emily as Holly Hills (both beautiful, sexy and girlfriends to Thomas and Greg)
- Sir Handel as Chirag (Spencer can't be Chirag!)
- Toby as Grandpa Heffley (both old, wise and father figures to Gordon and Frank)
- Daisy as Patty Farrell (both spoiled, selfish and rivals to Thomas and Greg)
- Whiff as Fregley (both wear glasses)
- Oliver as Ben Segal
- Duncan as Bill Walter
- Spencer as Robert Jefferson (both unapproved Thomas and Greg)
- Edward as Mr. Winsky
- Skarloey as Principal Roy
- Lady as Angie Steadman (Angie's voice suits Lady)
- Duck as Collin Lee
- Derek as The Cranium Shaker Guy
- Murdoch as Coach Malone
- Bertie as Sweetie
- Stepney as Jeff Kinney
- Caroline as Linda Jefferson
- Madge as Mrs. Hills
- Flying Scotsman as Mr. Hills
- Henry as Joe Heffley
- BoCo as Gary Heffley
- Diesel as Stan Warren (both devious and rivals to Gordon and Frank)