Who was Nikola Tesla, and what did he actually invent?
A Serbian-American engineer whose real contributions are substantial and are routinely buried beneath claims he never made — the internet-era Tesla is a character partly invented after his death.
What he genuinely did:
The rotating magnetic field and the polyphase alternating current induction motor — his central achievement. Practical AC motors made alternating current useful for industry, which is what decided the question of how electricity would be distributed.
AC power system patents, licensed to Westinghouse, which underpinned the alternating current systems that won out.
The Tesla coil, a resonant transformer producing high-voltage high-frequency output, used in radio work and still in teaching and demonstration.
Radio work. He demonstrated wireless transmission and held relevant patents; a 1943 US Supreme Court decision restored priority to some of his patents over Marconi's, though the ruling was narrower than it is usually reported to be, and the history of radio involves many contributors.
Remote control, demonstrated with a radio-controlled boat in 1898, which was genuinely astonishing to audiences.
Fluorescent and neon lighting work, and contributions to X-ray imaging.
What is overstated. He did not invent alternating current itself, which predates him; the "war of the currents" was a commercial conflict involving many people, not a duel; and his wireless power transmission project at Wardenclyffe, intended to transmit energy globally without wires, was abandoned when funding stopped — and the physics does not support the scheme as imagined.
The claims with no support: a suppressed free-energy device, a death ray, and earthquake machines. These come from late-life press interviews, in which he made increasingly extravagant announcements, and from later invention.
Why the myth grew. He died in 1943 in a New York hotel, in debt and largely forgotten, having been eclipsed commercially by Edison and by better businessmen. That combination — genuine genius, poor commercial fortune, eccentricity, and a dramatic decline — made him an ideal figure onto which suppressed-genius narratives could be projected.