Swack is an overweight man with balding red hair and a small, square beard. He most frequently appears wearing a blue and yellow suit with a green feathered cap.
Rentwhistle Swack first appeared in "The Beasts of Karn" on the planet Karn, poaching its numerous dangerous creatures and selling them to hunters looking for game. His operation was easily thwarted by the combined efforts of Buzz Lightyear and Dr. Ozma Furbanna, with Swack and his customers forced to work under Ozma as punishment.
Swack was next seen in "The Main Event" in the employment of technocrat Norbert Klerm, having arranged a battle on the surface on Sentilla VI for the latter's entertainment by spreading a fake story about a cargo ship full of V-Class Hyper Bombs. Although Swack's plan to lure Buzz Lightyear and intergalactic criminal Torque into the fray succeeds, his efforts also unintentionally attract the attention of Evil Emperor Zurg. Terrified of the Emperor, Swack quickly attempts to flee, only to be halted and bribed into confidence by the overconfident Klerm, who declares his robots can provide enough challenge to keep them safe. Klerm's claims fail to hold up, with their ship soon assaulted by Zurg, who is less than pleased at their deception. Swack and Klerm are nearly killed during Zurg's attack, with the latter callously discarding Swack to save his own skin. Although Buzz manages to save both Swack and Klerm, he is annoyed by Klerm but doesn't hurt him because of his job. However, Swack attacks his former employer in retaliation for repeatedly putting him in danger, an act that the amused Buzz chooses not to stop for the time being.
Swack is next seen in "Downloaded", where Zurg has posted a galaxy-wide bounty for XR, who has the entirety of Star Command's computer systems and databanks stored in his head. Desperate to move back into Zurg's good graces after the events on Sentilla VI, Swack bribes the Grounders who have just captured XR for his bounty with double that of the bounty itself. The Grounders gladly relinquish XR to Swack for his offer, but Swack's efforts to escape with the robotic ranger fail once Team Lightyear boards his ship. While Swack attempts to cancel the check he handed to the Grounders, his ship is suddenly attacked and destroyed by Warp Darkmatter, though his life is saved by Mira Nova.
Charismatic yet weaseling, Swack is a deeply greedy man, but is well aware of moments he is in over his head. His fear of Zurg was great enough to push him to spend an enormous amount of money just to keep him out of the Evil Emperor's target sights.
Swack possesses no extraordinary abilities or knowledge, but prides himself as an entrepreneur and business man.
- "Greetings, and welcome lovers of the unusual! I am Rentwhistle Swack, your host for the Thrilla on Sentilla! A classic battle of good versus evil!"
- "Right! So just settle back and- ZURG?! Okay! We gotta get outta here! Now! Let's move! Come on everybody! Quick like bunnies!"
- In the credits of "The Main Event", Swack's name is incorrectly given as "Rentwhistle Swank", despite being written as Swack in "The Beasts of Karn." In "Downloaded", he is simply credited as "Rentwhistle".
- Swack's voice actor, French Stewart, previously voiced Icarus in Disney's Hercules: The Animated Series.