Elementary Cellular Automata are simple models used in computational theory and mathematics. They consist of a one-dimensional array of cells, each of which can be in one of two states: on or off. The state of each cell changes based on a set of rules that consider the states of the cell and its immediate neighbors. These automata are defined by a rule set, typically represented as a binary number from 0 to 255. Each rule determines how the cells evolve over time, leading to complex patterns from simple initial conditions. John von Neumann and Stephen Wolfram are notable figures in the study of cellular automata.