Avengers #21

Thor, Iron Man, Captain America, and Black Panther charge across a landscape of smoldering rubble on this George Pérez cover for Avengers #21 (1999) — lightning crackles from Mjolnir, repulsor beams glow green at Iron Man's hands, and Cap's shield-bearing fist surges forward with unmistakable purpose. The headline "The Avengers Go to War!" sets a suitably urgent tone for Part Three of "Ultron Unlimited," and Pérez renders Earth's Mightiest Heroes with the kind of dynamic energy that made his work on this title so beloved. At $1.99, this is late-'90s Marvel assembling its heaviest hitters for what promises to be a pivotal chapter in one of the team's most intense confrontations.