The Marx Brothers were a family comedy act, originally from NYC. They had success in vaudeville, Broadway and motion pictures. They were five brothers: Chico, Harpo, Groucho, Gummo and Zeppo; sons of Jewish immigrants from Germany and France. They came from a family of artists, so their musical talent was encouraged from early on. All of them could play instruments and/or sing. Only Chico, Harpo and Groucho really developed their stage persona, as Gummo and Zeppo weren't as invested in acting. Gummo didn't appear in any of their movies and Zeppo appeared in some, but eventually left.
Here are the four Marx Brothers in character. From left to right: Chico, Groucho, Harpo and Zeppo.
The American Film Institute placed them #20 in their 100 Years... 100 Stars list, a list composed by 25 male artists and 25 female artists (see full list here). They also selected 13 of their films to be on their list 100 Years... 100 Laughs, where A Night at The Opera ranked #12 and Duck Soup #5 (see full list here).
Instead of writing everything I said about Duck Soup, given that it was improvised speech, I'll just leave you with the link to both Wikipedia and IMDb pages of this film.
Now here are the clips: