I’m pretty sure it wasn’t Marconi. He was just the first to get big Italian government backing for military applicaions.
It helps if you define “invent” and “radio”. Like all innovations, Marconi built on the work of others. However, he was the first person to devise a system that could transmit and receive electro-magnetic radiation farther than one kilometer – for this he shared the 1909 Nobel prize in physics. His key technical discovery was coming up with an antenna which produced groundwave signals, which is why his transmissions got out farther than any previous investigators. Once the technical of aspects of Marconi’s system were publicized, others were able to duplicate his success, and make important discoveries of their own.
Marconi was privately funded, mostly by British investors. He had first approached the Italian government, but was told they weren’t interest.
For more info on this topic I have a few hundred early radio history articles and extracts at my site United States Early Radio History.