The bravest character on the show has to be Morgan Grimes.
Even before he joined the spy game, Morgan was known to do some ridiculously stupid things. He reacts, rarely ever planning anything out. His impulsive nature also means he doesn't think much about insulting the wrong person (how many times did Casey nearly kill him?), or putting his foot squarely in his mouth.
He has short-person's syndrome, where he overcompensates for his height by wanting to do big-boy things. So he tends to aim big, lose big. What girl does he fall in love with at a young age? The super hot, super smart, destined to marry someone awesome Ellie Bartowski. Morgan has no chance but it doesn't matter. He dreams large. In his delusional mind, he just needs the perfect hook to get the gorgeous girl. His size, looks, intellect, or disposition be damned. Given the perfect circumstance, Morgan Grimes is a super model athlete.
And that mentality was nearly fine when the greatest harm he could do was injure his thumbs playing Call of Duty, or a black eye from hiding underneath Ellie's bed. Once he entered the spy game, Morgan Grimes became a much greater danger to himself.
Even before he knew that his bestest pal in the world, Chuck, was a spy, the second Grimes was aware of a spy operation at the Buy More, he volunteered himself to put a stop to it. That's insane! What innate skills did he have to pull that off? None. What training? Outside of video games, none to speak of and yet he went into it without a second thought.
It makes sense, though. Morgan doesn't possess much of a filter for his limitations. So he made for a very brave, if perhaps incapable, spy. He would put his life in danger for his friends, or for his country, without much consideration for his life. Because Morgan cares more about impressing those he respects, or keeping those he loves safe, than about surviving the next three seconds.
Morgan Grimes will die for you. Even if you won't die for him. Were he taller, or stronger, or more capable, he would be a super soldier. And for a brief period of time, he is one. During the time he is the Intersect, Morgan is probably at his happiest. All of his dreams become reality and he is able to do all things and be all things his dreaming mind told him he was anyway. One could even argue that douchie Intersect Morgan, when his brain is corrupted by a virus, is what Morgan would be like if not for all of his limitations.
His brain is massive. His size is small. He'd probably turn evil, if he'd grown to be tall.
Lucky for Chuck, Casey, Sarah, and his loved ones, Morgan turned out little, loyal, brave, and the guy you want around when you need someone to do something totally stupid to save the day.