It is undesirable for an airplane to bounce on landing—it could lead to a loss of control. The landing gear should not add to this tendency. A steel coil spring stores impact energy from landing and then releases it. An oleo strut absorbs this energy, reducing bounce.
The largest cargo airplanes in the world, such as the Antonov An-124 Ruslan, use oleo struts to allow for rough-field landing capacity with a payload of up to 150 tons. This design also cushions the airframe from the impacts of taxiing.
Cleveland Pneumatic Tool Company designed and introduced the first oleo-pneumatic shock-absorbing strut for airplanes, later called "Aerol" struts in 1926. Oleo struts have been in use for many decades. Oleo-pneumatic shock absorber technology has continued to be refined, for example with US patent US2959410 A, Jarry Hydraulics, in 1960.
Pneumatic systems like the oleo strut generally have long operating lives, and the construction is not unusually complex for maintenance purposes.