Conversation so far:
Why is Groucho Marx known for the mustache?
His distinctive appearance, carried over from his days in vaudeville, included quirks such as an exaggerated stooped posture, spectacles, cigar, and a thick greasepaint mustache and eyebrows.
Was there a way that Groucho Marx curled his mustache?
his was drawn onto his lip with grease paint, containing no hairs or bristles. In later life he grew his own, real moustache.
What about Groucho Marx's eyebrows make them notable?
a quick glance in the mirror revealed his natural hair eyebrows were too undertoned and did not match the rest of his face, so Marx added the greasepaint to his eyebrows and headed for the stage.
Are there any other interesting aspects about the Groucho Marx article besides the mustache and eyebrows?
The exaggerated walk, with one hand on the small of his back and his torso bent almost 90 degrees at the waist was a parody of a fad from the 1880s and 1890s.
Did Groucho Marx suffer ill effects from the walk?

Question: When did he start using the greasepaint for his brows and mustache?
Self-contained rewrite: When did Groucho Marx start using the greasepaint for his brows and mustache?