Johnny Cash is a true icon of American Music, and had one of THE most distinctive voices in Country. He doesn't hold a candle to Merle Haggard as a songwriter, though.
As to Death as a subject for music, why the folk tradition is just full of that from "Edward, Edward" to "1,000 Dollar Wedding". It can be schmaltzy (Green, Green Grass of Home), spooky (O Death), and jauntily bizarre (Knoxville Girl). In fact, songs like Pretty Polly and Knoxville Girl hold a special place in my heart with their twisted combination of love and murder. Reckon that's my Scotch-Irish ancestry. Or maybe the Cherokee.