'Smallville's Massive Villain Twist Was Finally Paid Off Years Later in the Arrowverse

A DC's Legends of Tomorrow episode confirmed that Curtis Knox, a villain on Smallville, is actually Vandal Savage.
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10 Despicable Acts That Prove Fortress Jor-El Was the Real Villain of Smallville

In Smallville, Fortress Jor-El is a source of conflict for Clark Kent. While the A.I. Jor-El is there to help, there are times it crosses the line.