Sir John Ambrose Fleming
Sir John Ambrose Fleming was the first head of England's first University Department of Electrical Technology (a few years later to be called Electrical Engineering), formed at UCL in 1885.
In 1904, while Pender Professor of Electrical Engineering at University College London, Sir John Ambrose Fleming invented the Thermionic (or Fleming) Valve. This was the first Electron Tube device and signified the birth of electronic devices.
This device, patented on Nov 16th, 1904 was the first electronic rectifier of radio waves, and enable the widespread introduction of commercial radio services. The original Thermionic valve is a two-element rectifier based on the "Edison effect" which Fleming had worked on some years earlier.
Sir Fleming also gave public lectures on a broad range of topics, which were massively popular and attended by captivated audience. Fleming’s considerable achievements are reflected in the numerous awards he received such as the Duddell Medal of the Physical Society and his knighthood in 1929.
When Fleming died in 1945 he bequeathed his collection to UCL, and you can view much of it online