- "You don't have to explain a thing... I'm Jeff. I came because you called me. I'm not very strong, really near-sighted, kind of shy, and I tend to be a little reckless. This is just the way I am... I hope you want me to be your friend... okay?"
- — Jeff
Jeff Andonuts (ジェフ Jefu) is one of the playable characters in EarthBound, the second to join Ness. Jeff is the only permanent party member who is unable to use PSI abilities. To compensate for that, he can repair broken objects to turn into useful machines and weapons for battle, although what exactly he can repair is based on his IQ level and the broken items he has in his inventory. He usually uses Guns as his primary weapons, along with bottle rockets and the aforementioned repaired gadgets such as the Hungry HP-Sucker, Heavy Bazooka, Neutralizer, and Shield Killer. He also has the Spy ability, allowing him to look up enemy attributes and snatch away their drop item if they have one.
Jeff is the genius son of the great scientist Dr. Andonuts, and attends the Snow Wood Boarding School in Winters, FoggyLand. Paula communicates with him telepathically to rescue them from captivity in Threed. After acquiring the Sky Runner from his father, Jeff travels to Threed and rescues Ness and Paula, securing his place as one of the chosen four.
Jeff appears in Super Smash Bros. Brawl as a sticker based off his clay model, with the distinct change of his outfit's color and that he is looking up. Attaching this sticker to the bottom of Ness or Lucas's trophies in The Subspace Emissary increases their PK attack by 24. He also appears as an Assist Trophy, launching bottle rockets at his opponents.
- Jeff's equivalent in EarthBound's prequel, EarthBound Beginnings, is said to be Lloyd. Both Jeff and Loid share similar roles in their corresponding games, in addition to having similar appearances. These similarities extend to both characters being very intelligent, skilled at building inventions and wearing glasses. They are also both unable to use PSI. In addition, both characters are found at schools.
- Jeff's equivalent in EarthBound's sequel, Mother 3, is said to be Duster. While neither Jeff nor Duster share similar roles in their corresponding games, in addition lacking similar appearances, there are similarities extending between each other's use of tools as their primary weapon and their lack of PSI.
- Jeff is the only permanent party member other than Ness to never temporarily leave the party.
- Using the Don't Care naming option, possible names for Jeff are "Jeff", "Dan", "Henry", "Isaac", "Ralph", "Sean", and "Rob".
- Jeff seems to have a very strained relationship with his father; if Jeff mentions him, he will often say "Dad", followed by, "I mean, Dr. Andonuts," indicating something along the lines that he does not consider Dr. Andonuts to be a fatherly figure. Also, when Jeff stops by Dr. Andonuts's lab, he doesn't seem to recognize Jeff, nor does he make any sort of fatherly actions. Something similar happens when Jeff is in Ness's party and they go see Dr. Andonuts so they can get to Summers; Jeff is mostly unnoticed by Dr. Andonuts. This troubled relationship seems to be resolved after Giygas is defeated, however.
- Jeff cannot perform any smash attacks with his regular weapons (Jeff mainly uses Guns and they do not hit anything like baseball bats or etc. do). However, in Mother 1 + 2, Jeff can hit SMAAASH!!es with his guns. This is probably an error in the game's programming.
- Jeff's sprite's glasses appear as if Jeff was looking diagonally. This is more noticeable in Mother 1 + 2 because the Game Boy Advance more easily shows pixels than an SNES.
- In the Mother 1+2 Art Book, Jeff is shown in concept art to have been wearing a red t-shirt and brown shorts before using his finalized outfit, which made him look very similar to Lloyd. He is also shown by himself with a yellow Bicycle several times, which does not occur during the game.
- Jeff is the only character in Earthbound that the Camera Man can take a picture of without Ness. (As the picture in Brick Road's dungeon is avoidable if you simply don't read the sign, therefore meaning you can return later to take the picture with Ness if you so wished.)
- It has been speculated that Jeff's father, Dr. Andonuts, may be Loid from Mother (Earthbound Beginnings). This is due to similar hair color and the fact that they both hide in trash cans when scared.
- Jeff's last name is a reference to the an-doughnut, a Japanese donut (or doughnut) filled with red bean paste. It is unknown when the an-doughnut was first made.