The Robotic Modular Leg (RML) is a modular leg mechanism that is designed to reduce the complexity, cost, and control of legged mobile robots. The RML enables the resultant robot to perform forward and steering locomotion with fewer actuators than conventional legged robots. The proposed mechanism can be interconnected to two identical modules to form a biped and four identical modules to form a quadruped robot. The RML is composed of a double four-bar mechanism that maintains foot orientation parallel to the base and decouples actuation for simplified control, reduced weight and lower cost of overall robotic system. A passive suspension system in the foot enables a stable four-point of contact support polygon on uneven terrain.