Legendaries

Since Gen 1, each Pokemon game has introduced a class or group of extremely rare and powerful Pokemon known as legendaries. These had no evolutions(with the exception of Manaphy, which had an egg pre-evolution Phione). These Pokemon also had characteristically low catch rates with the lowest being 3 and had base stats of a minimum of 600. Pokemon aficionados have made it a point simply to catch them in every game not just to strengthen their team, but to also add to their prestige. Each Gen came up with more and more evolutions symbolizing everything from weather to even antimatter(Giratina). Except for in Gen 1, the player's character will always encounter a legendary as per the respective story line where usually the antagonists with their teams try to misuse the Pokemon's power. The latest legendary to be released by Nintendo is Hoopa, a dual Ghost/Psychic type in Gen 6. Legendaries also tend to have cool abilities which none other have which gives them an undue advantage in battle like Kyogre's Drizzle, which makes it rain and boosts the power of its water moves by 50%. Some legendaries are extremely easy to find and even thankfully have low catch rates( some lower than even pseudo legendaries! Yes, damn you Beldum). Others can only be legitimately obtained via trade or through a Nintendo event like Jirachi and Mew. This probably adds to their mystique. I personally also think that the best place to catch legendaries is Spear Pillar, not only because you can catch the creation trio and Arceus there, but because of the animation and the fact that you get to go to the Distortion world. Other legends are also good, like Yveltal, which is badass.