A magnetorheological (MR) actuator device comprising two or more MR actuator units. Each of the MR actuator units may include a motor, an MR fluid clutch apparatus operatively coupled to the motor to receive torque from the motor, the MR fluid clutch apparatus operable to generate a variable amount of torque transmission when subjected to a magnetic field. An output member is provided, a transmission operatively coupling the at least two MR actuator units to the output member, for the output member to receive torque from the MR actuator units. A controller for controlling the two or more MR actuator units to drive the output member, the controller driving the output member in at least an antagonistic mode in which the MR actuator units transmit torque in opposite directions to the output member. A collaborative mode may be provided to combined the torque of the two or more MR actuator units in a common direction on the output member.