- "Let's learn a BORING math lesson!"
- ―Mr. Jacob
Michael Jacob (known simply as Mr. Jacob) is a supporting character in Sibling Rivalries. He is the 5th/6th Grade math teacher at Wisconsin Elementary School. Mr. Jacob wears a jacket with a J on it, shorts (after "Field Trip Gone Wrong!", he wears pants instead), and sunglasses.
A running gag in the series is that whenever Mr. Jacob and his classroom appears, there is always funny drawings that are written on his whiteboard (such a stickman with the words "Me Dum!", a crudely-drawn monster about to eat a stick man, and even an easter egg Cletus that appears frequently).
- His possible wife may be Mrs. Jacob, but it is uncertain, as Mr. Jacob lives in Wisconsin, and Mrs. Jacob in Canada. The two may have been in Canada during 2012, and in Wisconsin in 2013 on.
- Sibling Rivalries Pre-Series
- Sibling Rivalries (Season 1)
- Sibling Rivalries (Season 2)
- Sibling Rivalries (Season 3)
- Field Trip Gone Wrong!
- Patrick McReary: School President
- Like Father, Like Sons (And Daughter) (non-speaking cameo)
- Sibling Rivalries (Season 4)
- Sibling Rivalries (Season 5)
- Sibling Rivalries (Season 6)
- Brothers For Life (cameo)
- Sibling Rivalries (Season 7)
- Packie The Prankster (name appears on a piece of paper only)
- Sibling Rivalries (Season 8)
- Sibling Rivalries (Season 9)
- The Mighty J! (speaking cameo)
Total Number of Series Appearances: 14