humanitarian, do-gooder, improver (noun)

someone devoted to the promotion of human welfare and to social reforms

addition, add-on, improver (noun)

a component that is added to something to improve it

"the addition of a bathroom was a major improvement"; "the addition of cinnamon improved the flavor"

improver (Noun)

Something that, or someone who, improves

improver (Noun)

A substance added to cause improvement (especially to a foodstuff)