Marshall is an occupational surname, not having to do with anything military or martial, but stemming from the Norman French for someone caring for horses. It's been used as a first name since the nineteenth century and has been on the Social Security list since it started to publish its data in 1880. Marshall currently ranks at Number 345.
Marshall is the real name of rapper Eminem, and it got some attention during the heyday of communications maven Marshall McLuhan. Peyton Manning named his son Marshall, and Jason Segel played the character of Marshall Eriksen on How I Met Your Mother.