That's because he's a Companion. Has his own thread here, and his own page on Obsidian Portal.
He normally wears Heavy Leather Armor. But if he's offered chain mail that's lighter than what he's wearing now, he will accept...especially if it's the same kind that Alexei's already created for Laetitia and Wilhelm, with the maga's permission, checks it out to be sure it's not too clunky or clanky.
He will remove his leather armor (which I'm assuming is his top layer) and put the chain mail on over his clothes, placing his own armour in the cart.
I don't believe Alexei has worked with Wilhelm before (Wilhelm was in the "Remains Of Those Who Came Before" and the "All The Leaves Are Brown" threads before this one).
Wilhelm reaches up to touch his bow with one hand and places his other on his knife. [color=green]"I am armed enough, magus," he says. (As an aside, once he realizes that Alexei is speaking with a German accent, he will speak in his native German as well – he speaks no Latin, and his French is a meager 2).
He will travel about 50 to 100 paces ahead of the main party, keeping his eyes and ears open for anything out of the ordinary. Visual spot check: Per 2 + Awareness (in the forest) 4 + Keen Vision 3 + Ways of the Forest bonus 3 + die roll of 1 (followed by die roll of 10, for 20) = 32. (Hey, that ant has acne!). Hearing spot check: Per 2 + Awareness (in the forest) 4 + Sharp Ears 3 + Ways of the Forest bonus 3 + die roll of 0 (not a botch, though) = 12.