Rubik's Revenge is a 4x4 version of the classic Rubik's Cube, which features an additional layer of smaller cubes, making it more complex than the original 3x3 cube. It was invented by Ernő Rubik in 1981 and is known for its challenging puzzles that require different strategies to solve due to the absence of fixed center pieces. The cube consists of 56 smaller cubes, or "cubies," and can be scrambled in numerous ways. Solving Rubik's Revenge involves understanding advanced techniques, such as parity errors, which do not occur in the standard 3x3 cube. It remains popular among puzzle enthusiasts and competitive solvers.