Dill is native to western Asia and the eastern Mediterranean region. The earliest known mention of this herb dates to about 3000 B.C., where it was mentioned in Egyptian medical texts.
The Romans considered dill to be a sign of good luck and the ancient Greeks viewed it as a symbol of wealth. It was used for protection from witches, evil and bad luck. But it's greatest use, was in the kitchen.
Dill was traded and transported across Asia, into Europe and eventually to the Americas. The herb evolved in the different cultures where it was used, providing us with a number of herb cultivars. As far as I know, dill has never been hybridized, but so-called "new" dills have come on the market through the process of selecting out desirable characteristics.
For example, Thai Dill (Thai Name: Pak Chee Laos) is a somewhat regional variety, used in seafood, and with fresh oysters. Thai dill is slightly more yellowish than the dill you may be used to, and has fleshier fronds that almost seem succulent. You can find Thai dill at Baker Creek Seed Co.
Here's a rundown of several dill cultivars. Some varieties are best suited for seed production, while others are better choices for more leaves (dill leaves are called, "dill weed.")