A heavy fall; esp. in phr. to come (or go) a mucker, to come a cropper, to come to grief. (1851 —) . G.Mitchell I like old Jimmy boy and I wouldn't want to see him come a mucker (1974).
[From mucknoun, dung, dirt + -er; from the notion of falling into muck.]
mucker noun, US
A coarse, vulgar person. (1884 —) . F.ScottFitzgerald Why is it that the pick of young Englishmen from Oxford and Cambridge go into politics and in the USA we leave it to the muckers (1920).
[Perh. from German Mucker sulky person, gloomy fanatic or hypocrite (cf. obs. US sense, fanatic or hypocrite).]
mucker noun, Brit
A friend, companion, mate. (1947 —) . M.Woodhouse 'Is that my old mucker?' said Bottle. 'None other,' I said (1972).
[Prob. from to muck in to share tasks, etc. equally.]