Max Weinreich was a Russian Jewish linguist, specializing in sociolinguistics and Yiddis. His son is the linguist Uriel Weinreich.
He is known for popularising the phrase "A language is a dialect with an army and navy".1
His work also included translating and editing songs in Yiddish, like Yidishe folkslider mit melodyes.
1 It published in Weinreich's article Der YIVO un di problemen fun undzer tsayt, January–February 1945, pp. 13.
Full biography at The YIVO Encyclopedia of Jews in Eastern Europe.