Licklider was a psychologist who studied hearing, which is a strange background for the person most responsible for interactive computing. In 1960 he wrote "Man-Computer Symbiosis", arguing that computers should work alongside people in real time instead of chewing through punch cards overnight.
At ARPA he got a budget and used it to back a handful of university groups. He also wrote a memo to them addressed to the "Intergalactic Computer Network", half joking, describing machines all over the country talking to each other. ARPANET came out of that circle a few years later.
He didn't build much himself. His talent was seeing the shape of something early, finding the right people, and leaving them alone.