Christopher Tolkien

Christopher John Reuel Tolkien, was born on November 21, 1924, to John Ronald Reuel Tolkien, and Edith Mary Tolkien (January 21, 1889-November 29, 1971), their third and youngest son. He has taught at Oxford University, where his father was a professor, and is sole literary executor of his fathers works, which he edits and provides commentary on.

He drew the original maps for his father's The Lord of the Rings, which he signed C. J. R. T. The J. stands for John, a baptismal name that he does not ordinarily use.
[Sources: Wikipedia, back flap(s) of his publications.]