Christopher Tolkien is executor of the estate. He lives in seclusion in France and rarely even goes home to England.
He is extremely possessive of his father's work and doesn't think that they should ever appear in any other medium. He is very concerned about the works being perceived as literary masterpieces and thinks that movies will only dilute their presence. I find this ironic since Tolkien himself never really gave a damn what the snobs of the literary world thought of his books. He didn't write it for them after all. I have also heard that since Christopher helped his father proofread and edit the books that he believes that he is some kind of co-author but is bitter that he has never achieved the recognition he feels he is due.
For the record, Christopher has never seen the movies and refuses to acknowledge them in any way. His grandson Simon (I think thats the right name) publicly embraced the movies when Fellowship came out and attended the premiere in London. For this heinous crime, Christopher refuses to speak with him or even see his great grandchildren and hasn't relented to this day.
Simon was also kicked off the board that manages the Tolkien estate and apparently is even being written out of Christopher's will and won't receive any future royalties related to the estate or any inheritance at all.
I believe the rights to the Hobbit still reside with the Tolkien estate and I don't think they will ever let New Line make the Hobbit as long as Christopher is in charge. They will also never let New Line make a museum with all their props and stuff.
He is a petty, vindictive, and bitter old man. But I will at least say that while I think he is an ass, he has through sheer force of will prevented his family from legally squabbling over and ultimately selling the rights to his father's legacy for money. He has generally done a good job of preserving his father's legacy. But recently, especially in regards to the movies, he has totally gone off the deep end.