Most people consider me a joke or a loser

Most people consider me a joke or a loser. "What kind of criminal sends clues to the authority?!", "He must want to get caught!", "How does he make any money?". They put me on par with the Firefly, whose crimes don't make money, or that loser Killer Moth. Why, they ask, does the Riddler give out Riddles? Why do I do it again and again and again, when it only leads me to defeat after defeat?

They don't get it. I could have taken a job in ANY other field, legal or otherwise, and retired by the time I was twenty-five. I'm not boasting- I actually am that smart and determined. Hell, even working part time as a computer criminal/programmer, I've managed to accumulate a tidy nest egg. I wouldn't make Forbes list, but I don't have to worry about money and probably never will. Nor am I like the Mad Hatter, so tied up in my costumed persona that I'm incapable of a normal life. I admit it's nice to be a celebrity in Gotham, to skip to the front of the line at the Iceberg, but if my fame vanished tomorrow I wouldn't shed a tear.

So, why do I do it? Why do I continue to don my electric green suit and domino mask? Why do I continue to risk my freedom and my health if I have no need for the money?

Take this current caper, for instance. Right now Query and Echo are supervising the henchmen as they load up the truck with gold bars. However, given the extreme difficulty of fencing gold bars (requiring me to smelt the metal) and the extreme weight of the loot (meaning I can only take a relatively small amount of it), I'll probably end up taking a loss in the end. On the other hand, if Batman deciphers my clues I will almost certainly end up back in Arkham Asylum, most likely with a few broken bones. So why do it?

Because the game is all that keeps me from going mad with boredom.

I actually have tried giving it up. It was just after Batman had broken my legs for the first time- well, the first time he broke both at once anyway. I decided enough was enough- time for Eddie Nygma to retire to a quiet island in the Caribbean and leave the Bat to his own devices. I arrived in sunny, beautiful Jamaica and began my well-earned retirement. It took me only a week to sink into a deep depression under the sheer weight of my own ennui. I tried everything to regain that spark- sex, drugs, alcohol. Nothing helped.

You see, the downside of having an astronomically high IQ is that the mind demands constant stimulation. Simply put, if I don't challenge my brain regularly it starts flooding my body with the chemicals of depression. Playing Tetris and doing crosswords simply aren't enough; I've probably beaten the world record in Tetris, and have done enough crosswords that I can solve the New York Times one in less than seven minutes. No, as anyone can tell you, true stimulation can only be had in challenging ones equals.

But, I thought, that didn't necessarily mean I had to go back to Gotham. Surely there must be someone else who could prove worthy of matching wits with the Riddler. First I tried Lex Luthor- but Luthor, like the Joker, plays entirely by his own rules. I attempted a corporate takeover of one of Lexcorp's smaller firms- and was assaulted by thugs warning me to 'stay away from BioTekk'. No subtlety, no intelligence- just force. Luthor'd been in power for so long that he'd lost touch with the joy of a good game of cat and mouse.
I moved on to Ra's Al Ghul- thinking that surely the head of an international terrorist organization would be able to satisfy my need for an equal. Wrong. I paid Catwoman (good old Selina!) to steal some files from his headquarters, leaving behind a cunning riddle as to where to find them- I thought it was a good opening gambit. Instead, the old coot simply put out the word that he would pay five million dollars for the return of his papers. Again, no intellectual challenge, just solving the problem with money. Naturally, I burned the damned papers.

No, the years have made it plain that only Batman can truly match my wits and cunning. They have also shown me that without that battle, I would lose that which is most precious to me- my mind. When I'm the Riddler- the puzzling menace of Gotham City- I feel great and powerful and happy. Without Batman there is no Riddler, only Edward Nygma in a strange suit. I need Batman.

But, you ask, why send him hints and riddles? Why not rely on him to defeat me without help? Because without the riddles, we aren't the Riddler and the Batman; we're just two grown men in silly costumes playing cops and robbers. Also, I admit there's a somewhat more hedonistic motivation. Nothing gives me that pure joyous rush that I get when crafting the perfect puzzle to perplex the Dark Knight.

So, what's a few months confinement and a couple of broken bones when weighed against sanity and happiness?

Ah, I can hear the sound of smashing glass. Probably the skylight, he's always been fond of entering from above. I send the thugs in and signal the girls to start the engine, knowing that it will do little good. He's beaten my riddle and the puzzle I left at the bank, and he's far superior to me and mine in the physical arena. This round to you, Dark Knight, but the game goes on. And I wouldn't have it any other way.

He is my rival. My enemy. My sanity. My equal.

Batman.

A/N
I've always seen the Riddler as less of an enemy to Batman than a rival- and also as a BIT of a megalomaniac with delusions of grandeur. (He's also a complete pimp, but that's a story for another time). He doesn't hate Batman, in fact I wouldn't be surprised if he had no ill feelings for the Bat at all. He sees him as a rival, someone who is worthy of a game of wits. Kind of like the Joker, but not as extreme (or as cool)