Fleming valves, invented by Sir John Ambrose Fleming in 1904, were the earliest vacuum tubes. These glass-encased devices used thermionic emission to control and amplify electrical signals. 

They played a crucial role in early electronics, powering radio receivers and amplifiers, and were vital in the development of early computers and televisions. Though replaced by solid-state components, vacuum tubes still have a special place in audio and retro tech communities, known for their warm, analog sound and vintage charm.