He also became friends with slide guitarist Robert Nighthawk , which led to Hooker playing slide guitar and some performances with Nighthawk 's group outside of Chicago .
Also around this time , he met and developed a friendship with Robert Nighthawk , one of the first guitarists in Chicago to switch to electric guitar . Nighthawk taught Hooker slide-guitar techniques , including various tunings and his highly articulated approach ; Nighthawk would have a lasting influence on Hooker 's playing .