Magnetorheological semi-active suspension systems are widely used for vehicle vibration reduction, in which control strategy plays a crucial role. To mitigate body vibrations and optimize pitch characteristics, this study employs the Linear Quadratic Regulator (LQR) to control the six magnetorheological dampers of a six-wheeled vehicle's semi-active suspension. A 9-degree-of-freedom vehicle dynamics model and a random road surface model were developed. The Genetic Algorithm was utilized to optimize the weight parameters of the LQR for various control objectives. Vibration reduction performance was compared across three configurations: (1) passive suspension, (2) independent skyhook control, and (3) LQR-based cooperative control. Numerical simulations confirm that the LQR weights optimized under E-class road profiles at 36 km/h deliver over 31% overall vibration reduction versus passive dampers under diverse operational scenarios. Validation covers: (1) A to F class random road profiles, (2) velocities ranging from 10 to 40 km/h, (3) three damper parameter sets, and (4) three different sprung masses. Additionally, LQR-based cooperative control demonstrates advantages over skyhook control in resisting pitch and roll motions due to the simultaneous control of six dampers.