Friedrich __, Marx's benefactor and collaborator (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
engels
(Other definitions for engels that I've seen before include ". . . and his friend, Friedrich" , "Karl Marx's collaborator" , "Early Communist philosopher" , "political theorist" , "He co-authored The Communist Manifesto with Karl Marx" .)