Trigonometric functions became "mainstream" since the publication by Ptolemy (II AD) of trigonometric tables. To be sure he did not use our modern sine and cosine,
but a single trigonometric function, the chord ($=2\sin(t/2)$).
Modern definitions of sine and cosine were introduced by Indian mathematicians (Surya Siddhanta (V century AD), and reached Europe through Middle Eastern
mathematicians. After the fall of Constantinople, this knowledge quickly spread in Europe. The first treatises on trigonometry in Europe were written by Peuerbach and Johann Muller (Regiomontanus) in 1464. Copernicus of course used trigonometry extensively, as well as Kepler.
Theory of proportions has nothing to do with this, by the way.
You may look to Wikipedia: https://en.wikipedia.org/wiki/Trigonometry#History to begin with.