The Square Four, Leader, and Arrow motorcycles were all produced by the British motorcycle manufacturer Ariel Motorcycles. Ariel Motorcycles has a rich history dating back to 1870 and has manufactured a range of motorcycles over the years. The Square Four, introduced in 1931, was one of Ariel's most notable and innovative models, featuring a unique four-cylinder engine configuration with the cylinders arranged in a square pattern. The Leader and Arrow models were produced by Ariel in the 1950s and 1960s. These motorcycles had distinct styling and engineering features for their time.