And if not ruthless, at least tenacious. It was his dogged persistence, not any tactical brilliance, that won for the Union.
Every other commander of the Army of the Potomac, upon being defeated on a single day, would retreat back to their base. Grant, beaten at the Wilderness, didn't retreat, and instead began working his way around Lee, boxing him in. In a few weeks, Lee was reduced to end-game stalling.
The way Lincoln went through generals, there is enough evidence to argue that Grant simply came along at a time subsequent to a number of years of attrition. In other words, while he certainly wasn’t ignorant, he happened to be in the right place at the right time. If he was a genius, he would have also been a President with memorable accomplishments. Instead he was a one termer. He and General Sherman orchestrated Sherman’s “March to the Sea” which was a scorched earth policy that instituted a war on civilians in order to cut off supplies to the Southern armies. There was no Southern invasion of the North and there was little to no Southern support for it until Gettysburg. That only took place after Sherman’s March.