|Jonas Venture Jr.|
|"You can’t do that here. You’re cheapening the memory!"|
|1st appearance:||Dia de Los Dangerous!|
|Voice Artist:||James Urbaniak|
Jonas Venture Jr. was the brother of Rusty Venture and son of Jonas Venture Sr. While in the womb Rusty absorbed the entirety of his brother and unwittingly kept him there for about forty-three years. Jonas Venture Jr. or J.J. is considerably more successful than his brother and he is also a much more adept scientist. He is similar to Jonas Venture Sr. in everything but stature.
When Jonas was unwittingly removed during an operation his goal became to reclaim his life and end Rusty's. J.J used machinery from the lab to make a giant mechanical body for himself and attacked Rusty in order to claim the stewardship of the Venture legacy. After the attack was foiled by Brock Samson, the two brothers came to an agreement and Rusty allowed Jonas Jr. the use of Spider-Skull Island as a headquarters.
To replace/augment his stubby arm, Jonas was given a cybernetic one by Master Billy Quizboy, as well as a secret experimental jet much better than his brother's, along with countless other amenities. He soon began solving problems his brother could not, insisting that he take half of Rusty's government contracts off his hands.
Later, he assisted in the assembling of his father's greatest invention; which was only to be activated once, at a planned time, as the human race was not yet ready for it. During the adventure, the Ventures found The Pirate Captain is employed by Jonas as the captain of the X-2. In the aftermath, Sally Impossible revealed her attraction to Jonas and soon moved in with him at Spider-Skull Island along with her son Rocket and cousin Ned.
In the Season Four episode, Handsome Ransom, the Pirate Captain reveals that Jonas Jr. is building the Gargantua-2 (successor to the ill fated Gargantua-1) in the "Watchamacallit, the STRATOSPHERE!" This is later mentioned again in "What Color is Your Cleansuit?" when Jonas contacts Rusty to remind him that he was contracted to buld the protective force field for the space station.
In order to get Gargantua-2 fully financed and built, Jonas unfortunately sought the help of The Investors. During this time he also discovered that his body was dying from cancer caused by his genetic makeup including many of Rusty's recessive genes. When Gargantua-2 was finally opened to the public he knew his time was short so he made up with his brother and set the rivalry separating them aside. When the Revenge Society attacked Gargantua-2 and took out the force field protecting the station from asteroids Jonas, with the help of Rusty, Dean, and the newly recovered General Triester, managed to stabilize and evacuate the station long enough to save everyone on board. Jonas then piloted the jettisoned overloading nuclear power core into space. Jonas and Triester were on the station when it overloaded and presumably perished in the blast. In accordance with his will a memorial service was held for Jonas at the Venture Industries compound, complete with a requested performance of the Crash Test Dummies's "Mmm Mmm Mmm Mmm." His will also bequeathed Spider Skull Island and a sizable inheritance to Sally Impossible and his Venture Corporation and their new HQ in New York City to his brother Rusty.
 Episode Appearances
- Dia de los Dangerous! (as fetus)
- Eeney, Meeney, Miney ...Magic! (as fetus)
- Return to Spider-Skull Island
- Powerless in the Face of Death
- Twenty Years to Midnight
- Guess Who's Coming to State Dinner?
- The Doctor is Sin
- Tears of a Sea Cow
- Now Museum - Now You Don't!
- The Lepidopterists
- Bright Lights, Dean City
- What Color is Your Cleansuit?
- All This And Gargantua-2