Continuing my search for the Wesen of 'Grimm' in other TV series....
Nathan was a tail section survivor of Oceanic Flight 815. He was suspected by Ana Lucia of being one of the Others, due to his secretive behavior (which was probably due to his personality), and was killed when his neck was broken by Goodwin.
Nathan claimed he was in the tail section of the airplane at the time of the crash and was in the bathroom for most of the flight. Little is known about his life before boarding the plane, except that he stated he was on a company retreat in Australia and stayed behind to 'sight-see', and claimed to be from Canada, like Ethan.
While originally none of the other survivors were suspicious of Nathan, that did not last long as people began to grow suspicous after the second raid. Ana Lucia's suspicion that Nathan was "one of them" led her to throw him into the pit.
Nathan spent four days in the pit continuing to maintain his innocence. While in the pit he survived due to Mr. Eko giving him food. After Ana Lucia promised to begin cutting Nathan's fingers off the next day, Goodwin freed Nathan and then killed him by breaking his neck. He hid the body in the jungle. Goodwin later defended his actions by claiming Nathan was "not a good person". He also suggested that, if she tortured Nathan and he still didn't confess, Ana Lucia might finally start to believe he was telling the truth, and look for other suspects, putting Goodwin at risk of being discovered.
As you can see, Nathan's last name is not listed.
I put it to you that it was Steinkellner.
If so, Nathan had a twin brother named Timothy Steinkellner. And both of them were Klaustreich, Wesen who resembled humanoid alley cats in their native form.
Nathan's Wesen qualities were not detectable, not even in death. As we saw in the 'Grimm' episode "Love Sick", the bodies of two Wesen were discovered by the police and all of their "CSI: Portland" examinations still pointed to them as being human.
So after Goodwin snapped his neck, Nathan's body would still have retained his human form.
Nathan's brother Timothy must have moved down from Canada to just outside of Portland, Oregon, with his "wife" Robin. (She was a Seltenvogel, a bird-like Wesen. He was an alley cat...... It was never going to work; think of the children!)
I would not be surprised to learn that Nathan was not the first Wesen on The Island, but I'm not going to be the one to keep looking. I've got this candidate from 'Lost' and that's all I need for this unofficial connection to 'Grimm'.
So far, we've got 'Lost', 'The Wonderful World Of Color'/'The Jack Benny Show', and 'Law & Order: SVU'. I'm sure we'll sniff out more....