Gabriel's a nice guy, friendly, not above a tease or two. He's a prime example of Good Is Not Soft; he's merciless in the field. He's strong but not Ares-level strong--he can rip people from limb to limb, can rip doors out of buildings, throw cars. He can make himself resistant to harm, but it's limited and requires a lot of strength.
He was picked up when he was fifteen and brought in, then traded to the US corps for someone/something (he's originally British). So he's been around a while.