Albertus Magnus is typically credited with being among the first to produce and recognize arsenic in a relatively pure form, around the mid-13th century. He did not “discover” arsenic as a natural element from scratch, but his work is the earliest well-documented demonstration of isolating arsenic in a laboratory-like context by heating arsenic-containing minerals (notably orpiment) with soap, which yielded a purer form of arsenic. This achievement laid important groundwork for later chemical understanding of arsenic and its properties. The broader historical record shows arsenic compounds were known long before Magnus (in ancient and medieval times), but Magnus’s contribution is often framed as the first credible isolation of the element in a recognizable metallic form. If you’d like, I can provide a concise timeline with key figures and milestones.