anybody know where this person is? i want to get the sunlight straight sword off him so i can start upgrading it but i can't find any information on where he is located.

He's in an area right across the entrance from the dragon bridge. You get there after you beat the Taurus demon, I think. Though I'm not sure if you have to wait until later or not to get the sword drop.

I don't recommend killing him early on, as you can have him help you out against many of the bosses as a phantom.

He's super useful against the Gargoyles and the Gaping Dragon, imo.

If you're looking for the Astora Straight Sword, it's located in the Valley of Drakes near the Plague Dragon. You'll have to be careful though because it's literally under his claws. He does a poison AoE attack then swipes, so I'd recommend being quite quick with the rolling/dodging to get it. There is also a fantastic shield near him which I'd recommend to get while you're there.

To kill the plague dragon i stood 50 yards away from it and fired 120ish arrows at him. Take lots because he's got a shit load of HP, it just seemed easier to do at the time!