I knit the hat from a kit available from BellaKnitting.com I made this had for him to wear in the hospital, and it was the inspiration for the rest of the costume. I know Vikings didn't wear horned helmets, this is one of the fictional elements.
The chainmail shirt is made from (I think) liquid lame. Silver on a black background fabric. It also did not require hemming (score!). I made the edging from some woolie looking ivory fleece and fake suede to look like a shearling tunic beneath the mail. The belt is a strip of the fake suede stitched around the circumference of the tunic. It's very long so it won't ride up too much. In colder weather I'll put a plain white, long sleeved onesie beneath the tunic to keep him warmer, but the cloak was sufficient to keep him warm in our 60+ degree evening weather. This is probably also mostly fictional, but it looks good.
The pants and cloak are fleece - great because they're both warm and I didn't need to hem. I hate hemming. The cloak attaches to the chainmail shirt with buttons - I didn't want to have ties near his neck - and the buttons are reminiscent of the broaches historically used as fastenings in Viking clothing. I chose the colors red and green because they were also used in Viking clothing.
He doesn't have weapons or shield because I didn't have time to make them and because GeekBaby is still too little to hang onto stuff. I might make some next week before Halloween, in which case I'll update this slideshow.