Definitions for do-gooderˈduˈgʊd ər, -ˌgʊd-
Random House Webster's College Dictionary
do-good•erˈduˈgʊd ər, -ˌgʊd-(n.)
a well-intentioned but naive and sometimes ineffectual social reformer.
Origin of do-gooder:
humanitarian, do-gooder, improver(noun)
someone devoted to the promotion of human welfare and to social reforms
One who advocates or performs what they believe to be the morally superior course of action, even in the face of overwhelming experience or factual evidence that its effect is only irrelevant or harmful.
Prohibition in the United States was an unsuccessful attempt by do-gooders to save people from the dangers of alcohol, whether they wanted to be saved or not.
Origin: From do + good + -er.