With his masterfully grown sidefuzz flowing so perfectly into his under-the-nose walrus-spotch, General Ambrose Burnside seems suitably named. In fact, I'd always thought it was remarkable that his last name sounded so much like the man-growth that he wore so proudly.
I shouldn't have been surprised, then, to learn that it is not a coincidence: The word sideburn does, in fact, come from Burnside's name. Initially, the name Burnside became burnsides, referring specifically to the Civil War-era variety of facial hair in which sideburns and mustache collided in a reckless orgy of facial hair. However, by 1887 (and only twenty-two years after the end of the Civil War), the elements of Burnside's name flip-flopped and began referring only to the before-the-ears hair growth whose borders stop long before those of the mustache began.
It makes sense, though, why the name caught on as a generic term: The association of Burnside's name with this particular style of facial hair has to be the most harmonious marriage of name and meaning since South African white supremacist Eugene Terre'Blanche, who, yes, was real.