Hard mode: you have to say why it's your bro. The template will be at the second post.

>first gen
Primeape was a real powerhouse for my team when I first started playing my first Red version. And he was also the first one I could manage to get at level 100, so...

>second gen
By the time GSC was launched, my father gave me a hacked version of Crystal, with weird names, moves, and even some Pokémon found in different locations than the original games. One of those was a Houndour that I found at the first route. He managed to be one of the most useful Pokémon I've ever had when evolved. Even manage to kick Lance's ass when I got there.

>gen 3
Blaziken is the bro of the bros. My favorite Pokémon even nowadays, helped me a lot through Sapphire and Emerald. His mega and hidden ability also made him even greater.

>gen4
Murkrow was also one of those who made me like even more my hacked Crystal version. Then came gen4 and he finally evolved. It could be a little bit better or faster, but still one of my real bros. Helped me out a lot in Sinnoh.

>gen5
Even if he wasn't at my team for the most part of my campaign, Hydreigon really helped me out at the Elite 4. The rest of my team was a real piece of shit, except for my Scrafty, and he handled with most of them. And his design is fucking awesome

>gen6
I've always waited for a lion Pokémon. Even if Pyroar wasn't my ideal of an amazing Pokémon, he was pretty great to use in-game, helping me a lot during my campaign. I even managed to use him in wi-fi battles, and it was pretty good, even with the low movepool.