As should be clear by now, progesterone and estrogen are closely interrelated in many ways.
Progesterone is a precursor in the normal biosynthetic pathway for estrogen.
Our understanding of progesterone will be enhanced if we understand estrogen a bit better. First, there is a semantic problem to clear up. Then, estrogen was found to be not one hormone but a group of similar hormones of varying degrees of activity, all made by the ovary. The three most important hormones of this estrogen class are estrone, estradiol, and estriol. In popular writing, however, each of the specific members of the class continues to be referred to as estrogen.