Gabor was born as Günszberg Dénes, into a Jewish family in Budapest, Hungary. In 1918, his family converted to Lutheranism. Dennis was the first-born son of Günszberg Bernát and Jakobovits Adél. Despite having a religious background, religion played a minor role in his later life and he considered himself agnostic. In 1902, the family received permission to change their surname from Günszberg to Gábor. He served with the Hungarian artillery in northern Italy during World War I. He began his studies in engineering at the Technical University of Budapest in 1918, later in Germany, at the Charlottenburg Technical University in Berlin, now known as the Technical University of Berlin. At the start of his career, he analysed the properties of high voltage electric transmission lines by using cathode-beam oscillographs, which led to his interest in electron optics. Studying the fundamental processes of the oscillograph, Gabor was led to other electron-beam devices such as electron microscopes and TV tubes. He eventually wrote his PhD thesis on Recording of Transients in Electric Circuits with the Cathode Ray Oscillograph in 1927, and worked on plasma lamps.