BioAn AT-RT Driver (also known as an AT-RT Scout) was a type of specialized Clone Pilot or
driver who was trained to manuever or drive an AT-RT (All Terrain Recon Transport) onto the battlefield into combat, or to simply scout hard-to-reach areas.
AT-RT Drivers replaced ARF Scout Troopers (or simply ARF Troopers or Scout Troopers) during the second-half of the Clone Wars, and were far more intelligent and had better survival skills as opposed to ARF Troopers. Their armor was recycled from variants of Phase 1 armor (such as ARC Heavy Gunner, ARF Trooper, etc.) and was equipped with Phase 2 armor enhancements. Many units in the Grand Army of the Republic (501st, 212th, 91st, 187th, 41st, etc.) deployed and had various AT-RT Drivers pilot or drive their fleets of AT-RT walkers into combat throughout the second-half of the Clone Wars between 20-19 BBY.
Their name (as implied) describes their specialty serving as Clone Specialists.
The design for the 41st Elite Corps. AT-RT Driver from Star Wars: Episode III: Revenge of the Sith was originally intended to be used as a design for a Turbo Tank driver or commander, yet eventually became the design for the ARC Heavy Gunner from the Clone Wars microseries, as well as the initial 41st AT-RT Driver character design.
The 501st Torrent Co. AT-RT Drivers are often confused or mistaken for Phase 1 ARF Scout Troopers, yet the upper helmet's visor design is actually inherited from the Phase 1 ARF helmet.
The 2013 Clone Wars "501st Legion AT-RT with ARF Trooper and TX-21 Tactical Droid" action figure set (obviously) incorrectly depicts the official name and design of the 501st Torrent Co. AT-RT Driver, aside from depicting a Season 2-based Tactical Droid as the droid who commanded the station above Umbara's surface in Clone Wars Season 4.
The K9 Clone Trooper shares a similar appearance to an AT-RT Driver.
Star Wars: Episode III: Revenge of the Sith (First Appearance)
Star Wars: The Clone Wars Season 4 (Various Episodes)