Thanks go to Skelethin and Cornuthaum for edit and some useful suggestions.
Disclaimer: I don't own Naruto.
1. Unlike his teammates, Jiraya really doesn't have a surname. Tsunade, already burdened with her relation to two Hokages and to the noble line of Fire, never cared for hers. Orochimaru's parents were disgraced nobles who shamed theirs. Jiraya never had one. It never bothered him either. He was Jiraya, it was all there was to it.
2. He wasn't born in Konoha, or even in the Fire country. Truthfully, he doesn't know where or when he was born - the first real memory he has is wandering through Konoha outskirts looking to steal something to eat, since he was hungry. Despite that, he still shared an apple with a loud, blonde girl he met afterwards, if only to just shut her up.
3. Just like he doesn't have a surname, Jiraya once didn't have a name. However, unlike most things in his life he had to fight for or steal to get, this one was freely given by a a bratty, self important blonde little girl who tried to boss him one second, and shared her dango with him a moment later. Tsunade never admitted that she had stolen the dango herself beforehand. A year later, they met a boy named Orochimaru. The rest was both history and legend.
4. It is a little known fact, but Jiraya didn't aim to be a ninja and he actually started the Academy rather late. He was a street urchin, thief and one of the dregs that one barely paid attention to. He was brash, mouthy and too smart for his own good. He was also too good a thief for his own good. Trying to pick pocket an ANBU captain was really stupid, though - even if he almost managed to get away with it. To this day, Jiraya is one of the two pupils having the dubious honor of being escorted to classes by ANBU, bound in ropes so that he didn't escape. The second one, many years later, was Uzumaki Naruto. Those two were the only academy students who were chased by ANBU on regular basis and who actually managed to run away. Sometimes.
5. He didn't have a blood limit or a bloodline. He didn't have a ninja family, like Tsunade's, or inborn genius Orochimaru had shown since day one - Jiraya climbed the steps of his ninja career on guts, determination and instinct of a born fighter. He would never have it any other way.
6. It is his own little secret that among the Sannin, he has the highest kill ratio. While Orochimaru was a cold, merciless master shinobi whose jutsu claimed enemies by the score and Tsunade could wreck entire armies with her bare hands alone, Jiraya was the best assassin of the three. His record of A and S-class assassination missions stands unsurpassed to this day.
7. He was always the fifth wheel in Team Sarutobi - always neglected for the genius of Orochimaru and noble born, absurdly powerful princess. He smiled, he joked - he never forgave Sarutobi for that as long as the old man lived or after. Orochimaru and Tsunade never did, either - it was one thing they could really agree on.
8. It is a little know fact that, despite many thinking otherwise, Jiraya actually did have plenty of willing women in his life. While unabashedly perverted, often times corny, Jiraya can more than live up to the name of Gallant Jiraya - he treats every woman, be she a princess or a whore, with unabashed appreciation that he is always willing to prove.
9. No woman he took to his bed had ever walked away unsatisfied. Ever. However, his greatest satisfaction lies in the fact that he had never made any woman he had been with unhappy. If there was one thing he hated, it was seeing women cry. No woman cried because of him - in that respect, he was as gallant as a man can be.
10. Despite his numerous liaisons with women over the years, he only had two children - ironically, both of them women. Yuuhi Kurenai didn't know who left her the priceless scrolls containing genjutsu that masters would kill for and Tenten didn't learn who paid for her weapons, or who left the Soshuryu scrolls on her pillow when she graduated the academy until Jiraya's will was found, months after his death.
11. Icha Icha might be porn, that is true, but it is actually brilliantly written. It is also a proof of Jiraya's greatness as a writer that it is read by both men and women alike. It is a little known fact that the discovery and polishing of Jiraya's talents should be credited to Orochimaru, who spent countless hours beating the classics and proper writing skills into Jiraya's head with single minded ferocity only Hebi Sannin could show. Even lesser known tidbit is the fact that Jiraya's started writing porn on Tsunade's suggestion - something she can't live down to this day.
12. He was the first Toad summoner in centuries - no one knows where and how he got the ancient contract, or won the allegiance of the picky Toad Tribe - though Jiraya tended get a satisfied little smirk when an old matter of several hundreds bottles of sake that vanished from one of Konoha's storages was mentioned.
13. He was part of Legendary Sannin, but among them, he was the only one to actually earn the title of Sennin. It would come as a shock to most that his title as a Sage of Mount Moko is actually true. Even greater one would be the fact that, technically, Jiraya was not only a sage, but honest-to-kami priest. For Jiraya, there was no contradiction - Benzaiten is the patron of arts, wine, luck and love, after all. Besides, she was hot, as were her priestesses. That was all the justification he needed.
14. In the typical Jiraya fashion, he left that, like many other things, to Naruto, leaving him as a head of an order consisting almost entirely of beautiful women. Though for Jiraya, that was a mere formality, really. After all, Benzaiten was a goddess of luck as well and seemed to love the blond brat more than anyone else. He was right.
15. He took care of every one of his children, both those of his blood and not. He made sure Kurenai had a happy childhood, despite not knowing her father, as did Tenten. He took the best care of Konan he could and he had been father to Minato in all but name. The only person he ever failed was Naruto - he never forgave Sarutobi for that either. The Toad Sage also took care of his children even after his death. Kurenai inherited a lion's share of his huge fortune and the genjutsu scrolls he had gathered over the years that helped her to become one of the greatest masters of the art in the shinobi world. He used his considerable influence to force a pardon for Konan and made sure Tenten was given to the best teacher who'd let her develop in peace - he made sure that one of the most potent chakra weapons in the world fell into the weaponmaster's hands when she was ready as well.
To Naruto, he left all that made him the Toad Sennin and a little extra. It was fortunate that Tenten learned of the marriage contract after she developed an interest in the blond jinchuuriki. Jiraya took care of all of his children - but not without having his own fun at their expense, after all.
16. He was a man of secrets - he held more of them than any intelligence agency in the shinobi world. Among those most personal and guarded was the fact he could have probably circumvented the barrier Oto elites set during the invasion. He didn't. After all, Sarutobi always harped to him about handling his mistakes responsibly, didn't he? An even greater secret was the fact he didn't feel any remorse for that act.
17. He is the best Seal Master among the Sannin - arguably some of greatest masters of that craft ever born. He didn't have Orochimaru's twisted brilliance, or Tsunade's incredible theoretical knowledge and aptitude but he had more daring and imagination that both of them put together.
18. He loved Tsuande as much as any man can love a woman without wanting to bed her. He loved her as a prince his princess, as a thirsty man craves water, as a nameless man covets a name, as a dying man yearns for a cure. Friends was too tame, family not really applicable. They were Tsunade and Jiraya - that was enough for both of them.
19. As Naruto's godfather, he was supposed to take care of him - he didn't, which was largely Sarutobi's fault, and some of it his own. He never quite forgave himself for that, the Toads never really did either and Naruto never got over it as well as he pretended to. Yet they still mourned him greatly after his death - pulling some dumb shit not withstanding, the white haired pervert was family after all.
20. His teacher was called the 'God of Shinobi'. Jiraya, if anything, was a man among shinobi and despite great deeds, the awe inspiring power gained, blood spilled and lives taken, he never ceased to be one. Not for a moment. Overall, Jiraya thinks he got the better deal.