I have a friend from South Korea, whose parents used to own my favorite restaurant. They have retired, and no more restaurant but she taught me to make bulgogi, one of my favorite recipes. It's very tasty, but be prepared for dragon breath!!!
Combine the onion, garlic, sugar, ginger, soy sauce, and vinegar and sesame oil and pepper. Pour marinade over beef in a Ziploc bag or a bowl, toss to coat. Cover and refrigerate 2-24 hours, the longer the better.
Heat a grill. Remove beef from marinade and grill to desired doneness. The rib eye will cook fast and will be tender.