Answer : 3. "J. A. Fleming"
Explanation :

The first thermionic valve, also known as a vacuum tube, was invented by John Ambrose Fleming. Fleming, a British electrical engineer, developed the vacuum tube in 1904. The device, called the Fleming valve or vacuum diode, was a crucial component in early electronics and telecommunications. It played a significant role in the development of radio technology, serving as a rectifier and amplifier. The vacuum tube was an essential invention that paved the way for the advancement of electronic systems and was widely used until the development of semiconductor technology.