_ Felix Klein was a famous German mathematician. He lived during the years between Germany’s unification and the WWI. Klein’s main studies and works in the field of mathematics was about group theory, complex analysis, non-Euclidean geometry, and geometry. The following video will present details about his Erlangen Program in geometry, and how it was a big influence in mathematics during his time. It will explain what is the Erlangen Program, and it will also talk about the Euclidean geometry and the non-Euclidean geometry, both related a lot with Felix Klein’s works. He is also known for works in mechanics, asymptotic lines, W-curves… He is the creator of the Klein bottle, a representation of a four-dimension (4D) figure in the Euclidean space. Klein received two important medals to recognize his works. The first one was the De Morgan Medal, given by the London Mathematical Society in 1893, and the second one, Copley Medal, came in 1912, given by the Royal Society of London. Also, at the end of his career, Klein helped organise the Encyclopedia of mathematical sciences including their applications. This mathematical source is knows as Klein’s Encyclopedia nowadays.