General Sherman was the general that led a Union army through the Confederacy during the US Civil War. The army burned a mile (~1.7 kilometers) wide path across several states.

He hated slavery and slavers, and his actions to defeat the Confederacy made him a hero for the Union.

With the current climate in the US, his actions during the Civil War have made him sort of a folk hero again.

As this meme points out, he was, by no means, a good person. Just a tool of state violence who happened to be used to do something positive.

It's like praising a hammer that built a house for orphans then finding out it was used to kill homeless persons.