Linus, who since 2010 is an American citizen. Effectively, the US is probably the country closest to "owning" the Kernel, in that if the US wanted to put an abrupt cease to kernel development, they could, if only for a short period until the project re-organizes. I don't think any other country posses even the ability of doing so.
Any other person from any other country in the world can and could fork it in a heartbeat 100% legally. It wouldn't stop diddly squat, except that it loses its BDFL and finds another one in short order. There is absolutely zero the US could do about this.
