What Makes for a Nemesis?

Yesterday, Rachel Lovinger and I were discussing what the characteristics of a nemesis, partly inspired by an essay Rachel read by Chuck Klosterman entitled "The Importance of Being Hated." In other words, we wondered, how would someone qualify to be your nemesis? We came up with the following thoughts.

A nemesis:

1. Should be someone who people might normally assume you'd be friends with because of what you have in common
2. Should be someone you have respect, or at least grudging respect for, due to your respective strengths, weaknesses, and interests (nemeses may likely operate within the same field
3. Was a childhood or long-time friend, but you and your nemesis eventually had a parting of ways
4. Cannot just be an arch enemy. Wile E. Coyote is not the nemesis of Road Runner. They are simply mortal enemies
5. Is like the other side of a coin, making nemeses inseparable, perhaps meaning that someone could only ever have a single nemesis. (However, are numbers 5 and 6 below an exception? Or is Jay Leno simply evil enough to be a nemesis to two individuals?)

Who would qualify then as famous nemeses?

Arguably the following:

1. Sherlock Holmes and Moriaty
2. Superman and the Lex Luthor
3. Professor X and Magneto
4. Seinfeld and Newman
5. Stalin and Trotsky
6. Bill Gates and Steve Jobs
7. Larry Bird and Magic Johnson
8. Conan O'Brien and Jay Leno
9. David Letterman and Jay Leno

In his essay, Klosterman argues that The Joker is Batman's nemesis, but I'm not buying it. I don't see the Batman as admiring the Joker, who simply thrived on chaos and insanity. See Klosterman's essay, however, for more characteristics of what makes for a nemesis and for how to distinguish between a nemesis and an arch enemy. It's quite entertaining.

Who do you think also qualifies?