Gregor Mendel is well known for his work in Genetics.  
He was born Johann Mendel in a small town in Aurtria to a poor farming family.  Today, young people from poor families often join the military to get an education. In Mendel's time, they would join a monastery and that is what he did.   He followed the recommendation of his physics professor and entered a monastery.  He later continued his education at the University of Vienna, then returned to the monastery. 
He was inspired by both his professors and his colleagues in the monastery to study the variations that occurred in plants.  In a seven-year period he cultivated and studied 29,000 pea plants in the monastery gardens.  He learned that the differences that occurred were not arbitrary, but followed definite patterns.  His experiments produced  what later became known as Mendel's Laws of Inheritance with it's concept of recessive and dominant traits.
He later experimented with bees, but found them too difficult to control so he could get a clear picture of their heredity.
His work was largely rejected or ignored by the scientific community until after his death.  It didn't really get much notice until the early twentieth century.
In 1868 he became Abbot of the monastery and his administrative duties forced him to end his scientific experiments.  Especially when he had to fight a government attempt to start taxing religious institutions.