Trigonometry developed in many parts of the world over thousands of years, but the mathematicians who are most credited with its discovery are Hipparchus, Menelaus and Ptolemy. Isaac Newton and Euler contributed developments to bring trigonometry into the modern age.
The origins of trigonometry occurred in Ancient Egypt and Babylon, where scholars performed calculations with angles, measuring them in degrees. However, it was the Ancient Greeks who advanced the study, largely due to its relation to their interest in astronomy.
Hipparchus is often credited as the inventor of trigonometry because of his computation of the first table of chords. In order to calculate the rising and setting of zodiacal signs, he popularized the division of circles into 360 degrees and the calculation of chords by considering all triangles to be within a circle, with the three points each touching the perimeter.
Menelaus built on Hipparchus' work by expanding the knowledge of spherical trigonometry with an increased focus on transversals. Ptolemy expanded the table of chords that had originated with Hipparchus, calculating them at intervals of 1 degree. Subsequent work in India and in the Arab world led to the recording of half chords, and to the sine function. Later, the Germans defined trigonometry functions as ratios, Newton discovered calculus, and Euler used complex numbers to create his famous formula.