Polyethylene was discovered in the early 1950s by Giulio Natta. It is common in modern science and technology that the growth of the general body of knowledge can lead to the same inventions in different places at about the same time, but polypropylene was an extreme case of this phenomenon, being separately invented about nine times. It was a patent attorney's dream scenario, and litigation wasn't resolved until 1989.
Polypropylene managed to survive the legal process, and two American chemists working for Phillips Petroleum of the Netherlands, Paul Hogan and Robert Banks, are now generally credited as the "official" inventors of the material. Polypropylene is similar to its ancestor, polyethylene, and shares polyethylene's low cost, but it is much more robust. It is used in everything from plastic bottles to carpets to plastic furniture, and is very heavily used in automobiles.
CH3 H CH3 H CH3 H \\ / | | | | C == C -> -- C -- C -- C -- C -- / \\ | | | | H H H H H H
propylene monomer polypropylene polymer