Adam Clarke on Exodus 2:18

Reuel, their father - In Num 10:29 this person is called Raguel, but the Hebrew is the same in both places. The reason of this difference is that the ע ain in רעואל is sometimes used merely as vowel, sometimes as g, ng, and gn, and this is occasioned by the difficulty of the sound, which scarcely any European organs can enunciate. As pronounced by the Arabs it strongly resembles the first effort made by the throat in gargling, or as Meninski says, Est vox vituli matrem vocantis, "It is like the sound made by a calf in seeking its dam." Raguel is the worst method of pronouncing it; Re-u-el, the first syllable strongly accented, is nearer to the true sound. A proper uniformity in pronouncing the same word wherever it may occur, either in the Old or New Testament, is greatly to be desired. The person in question appears to have several names. Here he is called Reuel; in Num 10:29, Raguel; in Exo 3:1, Jethor; in Jdg 4:11, Hobab; and in Jdg 1:16 he is called קיני Keyni, which in Exodus 4 we translate Kenite. Some suppose that Re-u-el was father to Hobab, who was also called Jethro. This is the most likely; see Clarke's note on Exo 3:1.