2014, Czech Republic, My Own Stamps
Z = international rate
designers: Jaroslav and Michal Weigel
Jara Cimrman ... creator of the world's first round stamp
according to Ceska Post:
As a teacher in the Galician village of Nipple, Jara Cimrman met a local postmaster's daughter, Erika, T. who soon became his girlfriend and also the recorder of his ideas and principles. We know from Erika T's records that Jara Cimrman presented to the Austrian Imperial and Royal Post Office his plan of using field artillery for delivery of express mail. This innovative plan had the benefit of delivery within seconds to a given address. The disadvantage was that it also reduced the number of addresses. The plan was cancelled at the request of the Galician people. Inspired by the round postmark, Cimrman also designed a round postage stamp for these express consignments.
This is obviously not true as Jara Cimrman is a fictional character who spent his life in tireless pursuit of many disciplines. He is described as a "universal genius, inventor, sportsman, philosopher, criminologist, writer and philosopher". He first made an appearance on a radio show in 1966 and became an immensely popular Czech national hero.
His wikipedia page (which records some of his exploits) is here
for the letter C - Czech Republic, Cimrman