Jeff has appeared in some of the games that Dan has played, notably RollerCoaster Tycoon 3. Jeff was first named due to Dan's surprise at seeing a shark in the theme park's water, but quickly became a recurring joke when Jeff glitched into the air and appeared to be flying. This was usually due to the amount of platforms above water Dan placed or the glitchy frame-rate around Splasha.
In RollerCoaster Tycoon 3, Dan and Jeff are on somewhat friendly terms. However they can be more hostile to each other, such as in Far Cry 3.
Many procrastinators know about Jeff because of his magical ability to fly and his habit of eating unsuspecting park visitors behind Dan's back.
Jeff was first seen flying in Nerd³ Completes... Roller Coaster Tycoon 3 - Part 4. He was also seen flying in Part 3, however this was only due to Dan playing with water.
- Because the Jeff Isle area of Dan's theme park became too overcrowded, Dan relocated Jeff to the Aqaurium of DOOM, where he still lives to this day.
- In Nerd³'s Father and Son-Days Saints Row The Third - Part 3 Jeff is found dead on a wall. Dan responds by screaming "I WILL AVENGE YOU!". Dan then throws a lady off of a roof.
- At one stage in the series of NerdCubed Completes... RCT3 Jeff had a girlfriend who Dan called Jeffina. Sadly, Jeffina was killed by Dan when he accidently drained her water.