Many proofs of Pythagoras’s Theorem are known. The ones in this resource span a period of over 2000 years.
This approach is developed further in The Quintessential Proof.
This is due to Bhaskara (1114-1185), also known as Bhaskaracharya, an Indian mathematician and astronomer of great reknown.
This is due to James A. Garfield (1831-1881), who was the 20th president of the United States of America.
This argument appears in Euclid’s Elements, Book I, Proposition 47. Euclid lived from about 325-265 BCE, and according to Proclus (a later Greek mathematician, 411-485 CE), this proof of Pythagoras’s Theorem is due to Euclid himself.2