The Onslaught Saga is a significant storyline in the Marvel Comics universe, primarily involving the character Onslaught, a powerful entity born from the consciousness of Professor X and Magneto. This saga explores themes of heroism, sacrifice, and the consequences of unchecked power, as various X-Men and Avengers unite to confront this formidable foe. The saga began in the mid-1990s and includes several crossover issues across multiple comic series. It culminates in a battle where heroes must confront their own fears and the darker aspects of their personalities, ultimately leading to a resolution that reshapes the landscape of the Marvel Universe.