In 1975, Hervé Poulain commissioned American artist and friend Alexander Calder to paint the first BMW Art Car. This first example would be a BMW 3.0 CSL which Poulain himself would race in the 1975 Le Mans endurance race. Since then there have been 13 Art Cars in total, you can see them all here.
My personal favorites —
Alexander Calder, BMW 3.0 CSL, 1975
Roy Lichtenstein, BMW 320i Turbo, 1977
Jenny Holzer, BMW V12 LMR, 1999
Jeff Koons, BMW M3 GT2, 2010
Who would you like to see do the next BMW Art Car? I would pick @dalek to paint a race prepped i8