Trigonometry is fascinating in a way because it makes you think about how creative and innovative early human minds had to be to solve real world problems in front of them.
The ancient Egyptians developed an early primitive form of trigonometry to solve the logistical problems involved in building pyramids that could last for millennia; but, they lacked the concept of an angle measure.
It was mostly ancient Greek mathematicians who were studying the behaviour of heavenly bodies in the night time and trying to find out distances involved who put most of the pieces together to develop angle measurements.
Indian, Chinese and European mathematicians stretching out to the 1700's had to sharpen theories up and bring everything into a clearer and more detailed focus with all the innovative trig work they developed though.