appositive clause

Hi,
Can you tell me if these are correct?

I have used something similar to this in one of the inquiries I made in this forum.

1. A well-known sports star, known to have won medals in international competitions, came home.
2. A well-known sports star, who is known to have won medals in international competitions, came home.
3. A neighbor of mine, who is known to have won medals in international competitions, came home.
4. A neighbor of mine, one that is known to have won medals in international competitions, came home.
5. A neighbor of mine, one known to have won medals in international competitions, came home.
6. A neighbor of mine is a sports star, one known to have won medals in international competitions.
7. A neighbor of mine is a sports star, known to have won medals in international competitions.

I feel uncomfortable about nos. 1 and 7. I feel all others are correct. If no. 7 is not correct, then what is the reason? Why does it have to have a phrase like 'one known to have' or 'who is known to have'?

Also, do you feel for nos. 4 and 5, the phrases 'one that is known' is virtually the same as 'one known to have'??