Which Autobot transforms into a yellow Volkswagen Beetle?

The Autobot that transforms into a yellow Volkswagen Beetle is Bumblebee.

Bumblebee’s classic Generation 1 alternate mode is a small yellow Volkswagen Beetle, reflecting his identity as a compact scout and spy. His black-and-yellow color scheme also evokes the insect that inspired his name. Because he is smaller than many Autobots, stories often portray him as nimble, curious, resourceful, and able to enter places larger robots cannot.

The Beetle form is most strongly associated with the original toyline and animated series. Later versions changed his vehicle mode. In the live-action 2007 film series, Bumblebee is primarily a yellow Chevrolet Camaro, while the 2018 film Bumblebee restores the Beetle as an important part of his Earth disguise.

This vehicle change causes frequent confusion. A yellow Camaro is correct for several live-action appearances, but the question’s Volkswagen Beetle description points to the classic version—and also to the 1967 Beetle scanned in the 2018 film. Bumblebee is an Autobot scout, not the faction’s leader; that role generally belongs to Optimus Prime.