One of the original twelve American wizards and witches to volunteer to serves as aurors for the newly-created MACUSA (Pm).
Grimsditch and the other eleven original American aurors volunteered knowing that the job would be dangerous and demanding. Like most of his colleagues, Grimsditch did not survive to old age (Pm).
The descendents of the original twelve American aurors get special respect in wizarding America (Pm).
Robert = "famous"
Grimsditch = combination of "grim" + "ditch," possibly suggesting an early or unfortunate death.
Regarding etymology note on his surname, cf. his colleague Gondulphus Graves. -BB