Moses
Exodus 9:6ESV·traditional attribution

And the next day the LORD did this thing. All the livestock of the Egyptians died, but not one of the livestock of the people of Israel died.

Matthew Henry Presbyterian @wholebiblehenry

Here is, I. Warning given of another plague, namely, the murrain of beasts. When Pharaoh's heart was hardened, after he had seemed to relent under the former plague, then Moses is sent to tell him there is another coming, to try what that would do towards reviving the impressions of the former plagues.

Commenting on Exodus 9:1-7

John Gill Reformed Baptist @doctorgill

And the Lord did that thing on the morrow,.... Brought a murrain, or a pestilential disease on the cattle. This, according to Bishop Usher, was on the second day of the seventh month, which afterwards became the first month, the month Abib, which answers to part of March and part of April, and seems to be about the seventeenth of March: and all the cattle...

Jamieson-Fausset-Brown Reformed @jfbcommentary

all the cattle of Egypt died--not absolutely every beast, for we find (Exo 9:19, Exo 9:21) that there were still some left; but a great many died of each herd--the mortality was frequent and widespread. The adaptation of this judgment consisted in Egyptians venerating the more useful animals such as the ox, the cow, and the ram; in all parts of the country temples were...