From Wikipedia "
The AT-ST is a two-legged walker introduced in The Empire Strikes Back and featured extensively in Return of the Jedi. Due to their design and movement, they are often dubbed "chicken walkers".
The AT-ST model used in The Empire Strikes Back was to have more screen time; however, one scene depicting a snowspeeder shooting at the AT-ST model was ruined when the set's background shifted. For Return of the Jedi, ILM made the AT-ST design more detailed. Numerous models were created, including a full-sized AT-ST for on-location shooting. Director Richard Marquand and producer Robert Watts played the AT-ST operators for the scene in which Chewbacca (Peter Mayhew) and a pair of Ewoks commandeer an AT-ST.
Lee Seiler sued Lucasfilm in the mid-1980s, claiming that the AT-ST infringed on his copyright on what he called a "Garthian Strider", which he said he created in 1976 or 1977. The case was dismissed with the court noting that not only did Seiler not produce the supposed drawings at trial, but that the copyright came one year after The Empire Strikes Back debuted.
Star Wars guidebooks describe the AT-ST as a "reconnaissance or defensive vehicle [that] is lightweight and built for speed". Their agility allows them to defend the slower AT-ATs or support other Imperial ground forces. seat a pilot and co-pilot. AT-STs are armed with laser cannons on the "chin" and sides, feet claws for destroying small defenses and side-mounted concussion missile launchers.During the Battle of Endor in Return of the Jedi, the protagonists and the local Ewok tribes capture or destroy many AT-STs, which due to their precariously balanced design prove highly vulnerable to the Ewoks' primitive booby traps. In the Expanded Universe, AT-STs are often featured in Imperial attack forces. Video games such as Star Wars: Rogue Squadron and Star Wars: Shadows of the Empire include numerous AT-STs, and they are player-controllable units in several real-time strategy games. Several walker designs have been influenced by the AT-ST's design.