Complex sentence: Hermann Julius Oberth (25 June 1894--28 December 1989) was an Austro-Hungarian-born German physicist and engineer who was one of the founding fathers of rocketry and astronautics.
Split into simpler sentences: Hermann Julius Oberth (25 June 1894--28 December 1989) was an Austro-Hungarian-born German physicist and engineer. He is considered one of the founding fathers of rocketry and astronautics.