Targum Jonathan of the Former Prophets: Volume 10 in Bloomington, MN

The attribution, by the Babylonian Talmud, of this Targum to Jonathan ben Uzziel is suspect on several counts: among others, the silence concerning Jonathan in the parallel passage in the Palestinian Talmud, and the fanciful suggestion that Onkelos=Aquila and Jonathan=Theodotion. The attribution, therefore, is not to be taken as historical fact. The Talmud may have been attempting to enhance the authority of the Targum by claiming authorship by a disciple of Hillel, which Jonathan was.
It is generally agreed that the author of the Targum Jonathan is unknown; in fact, it is preferable to consider multiple authorship. For while language and translation techniques are uniform, there is variety from book to book.