After a series of other innovations involving radio, Fessenden invented sound over radio in 1906. Before then radio typically carried Morse Code signals. He created a company, NESCO, that struggled with IP, financing, and people issues.
The owners, including Fessenden, hoped to sell the company to AT&T or GE but that deal did not close. In 1910, the NESCO partnership broke down; Fessenden was ousted Jan. 8, 1911. Fessenden sued his ex-partners and RCA, that had eventually acquired the company including his patents in a deal he apparently did not approve of.
After 15 years of litigation Fessenden settled with RCA for $500K, albeit it with $200K of legal fees, leaving him $300K ($4.3M in 2018 dollars). http://www.ewh.ieee.org/reg/7/millennium/radio/radio_radioscientist.html Radio, with sound
de Forest Audion tubes are still in use to broadcast AM radio. While de Forest invented the Audion tube, it is Edwin Armstrong who figured out, and patented (unsuccessfully, in hindsight), its use as a radio transmitter and receiver. [See FM Radio for more detail.]