@Merry Mayhem. Agreed! That would lots of fun to have a companion like that.
As Oscar Wilde allegedly said "Imitation is the sincerest form of flattery that mediocrity can pay to greatness". Arneson and Gygax may have evolved the basic ideas around an RPG, by they proceeded to initially flesh it out with little regard to being inventive.
To be fair, creating detailed and consistent settings for fictional content is not a matter of a moments thought, so most great works of art or fiction build on prior art and history. The trick is to understand when you are overstepping the mark of plagiarism; Moorcock probably didn't care too much about his idea being reused, but TSR didn't get away with using Hobbits, Wargs and Balrogs for very long

Agreed. Might make list of what DnD took from Moorcock one day. Off the top of my head: the alignment system, the multiverse, need to kill it twice rules for demons and gods, sentient weapons, vampric weapons, elemental summoning, ships that sail on land, hand and eye of Vecna . . .
And yes you can wander into Plagarism - as was the case with the Witcher series. Amazon cancelled the Elric series because they thought another series with an inhuman, white-haired, red-eyed, sword fighting, wandering mercenary protagonist called the white wolf would confuse viewers. Grrr.