Really, the wonderful thing about Dungeons and Dragons is that you can be whoever you what, whereever you want. Let's say you want to be a midget who wields a hammer bigger than he is. With the right combination of feats and weapon, you could do that. (Playing a gnome barbarian with the feat Monkey grip, and the Gloves of Powerful build ought to do it. Match with a Minotaur greathammer for some real fun.)
Let's say you want to be a giant who throws his enemies around. Play a Goliath barbarian with the Martial Throw feat, and you can pull it off.
How about a ninja? You'll never be able to be Naruto, but for a regular ninja, a Human Swordsage comes pretty darn close. Pair it with a pair of short swords and the Two-Weapon Fighting feat for the best results.
How about something difficult? Let's say you want to be a master of two different types of magic, and be powerful in both. Start as a human wizard, and take the Precocious Apprentice feat. Next, take three levels of Druid. At that point, you can join the prestige class Arcane Heirophant, which will allow you to progress in both classes at the same time. Finish off with three levels of Mystic Theurge, and you have full spell-casting abilities in both classes.
Like I said in my previous post, you can be whatever you want, except possibly Naruto or Superman. So long as you work within the rules, there's a way to achieve what you want.
It's the same way with life. God has given us the greatest gift possible: life itself. With that gift, he's also given us the ability to choose for ourselves what we want to be. We choose that by what we desire. If I want to be a good person, I will. If I remember correctly, Andrew Carnegie said "It's no great trick to be rich, if what you want is to be rich."
So long as we want eternal life, we will eventually bend that way. It requires much, but if we want it more than anything else, there is nothing that can stop us.
For a really good talk about choise, read The Three R's of Choice. I love it.