The present invention provides an actuator comprising an actuator body, a piston relatively moveable within the actuator body, and a rod attached to the piston and extending out of the actuator body, the actuator body comprising a port for conveying actuator fluid, wherein the actuator also has a damping control portion provided with damping control fluid containing magnetic particles, wherein the piston or the rod is adjacent the damping control fluid, and a first electrical coil associated with the damping control portion, such that an electrical current supplied to the first electrical coil induces a magnetic field and causes the effective viscosity of the damping control fluid to increase, thus increasing the damping effect of the damping control fluid on the piston or rod. The invention also provides an aircraft assembly, such as a landing gear assembly, an aircraft and a method of operating an actuator.