Diphath was a son of Gomer, who was a son of Japheth and grandson of Noah. The parallel genealogy in Genesis gives the name as Riphath.
Diphath appears in the genealogy of 1 Chronicles 1:6 as one of the descendants of Gomer.
The difference between Diphath in Chronicles and Riphath in Genesis is a variation in the corresponding genealogical records. The source directs comparison with Riphath.