Every hero needs a villain, and every great story needs the perfect balance of good and evil. Whether that's Ahab and the White Whale or Mario and Bowser, you can't expect people to get invested in a character that doesn't grab them from the outset.
Not all debuts hit the mark, but when they do, they can be the catalyst that pushes a given creation from being an interesting distraction in a comic book story through the roof, and into the stratosphere - and a genre - where longevity is paramount. There's a lot of bad guys that are still going strong today, decades after they first raised their evil little heads.
Most of the new wave of villains over the past twenty-odd years have been quite happy to introduce themselves with one form of blood bath or another, but that is not what makes a great debut.
Whether they started off in Marvel or DC, the superhero genre is home to dozens of legendary villains. Most end up making a name for themselves somewhere down the line, but the best manage to make their first impression count.