Not directly a pig, but a land-living mammal where a different evolutionary branch developed into pigs (and cows, and a bunch more)

https://en.wikipedia.org/wiki/Even-toed_ungulate

https://en.wikipedia.org/wiki/Evolution_of_cetaceans

See also https://en.wikipedia.org/wiki/Pakicetus

I'd guess the ancestor was some thing resembling a hippo, like these sea surfing hippos from West Africa: https://youtu.be/ZvyBmXn7Euc

Also see this informative graphic: https://www.juneauwhalewatch.com/wp-content/uploads/2017/07/...

The hippo is a another close relative of the first water-loving mammals.

The docile hippo - one of the most dangerous animals in the world

Don't they kill more people annually than any other mammal?

I'd bet good money that humans have them beat.

Not a pig. Here is a fascinating article about how it seems to have happened: http://www.eartharchives.org/articles/the-evolution-of-whale...