Fatou and Julia published their famous works on the iteration of complex rational functions in 1919/1920 and 1918, respectively. Through the application of the concept of normal families by Fatou and Julia, functional-theoretic results became available for complex dynamics. This led to a breakthrough in understanding the global dynamic behavior of orbits: they discovered that the Riemann sphere is divided into two disjoint sets. One is the set known today as the Fatou set F(R), where two orbits exhibit similar behavior when their starting values are sufficiently close to each other. The other is the set known today as the Julia set J(R), where two different orbits display completely different behavior, even if their starting values are very close together.