In his last years, Grant worked with Mark Twain to write his autobiography. It is pretty clear that Grant was anything but a "callous bastard" or a "monster", particularly relative to others in that time period. Indeed, many of his political and personal problems stemmed from being too willing to trust people, many of whom were unsavory characters. (Grant ended up being bankrupted after being defrauded of his savings and had to sell all his war memorabilia, and part of the reason he wrote his autobiography was to raise money for his family before he died.)

It's a really interesting read for anyone.

There's also little evidence that Grant was a drunk during the Civil War; many historians believe that was propaganda spread by the Confederates and by political rivals in the north, which was based on his problems after the Mexican-American war. The accounts of people who were actually with Grant during the Civil War don't support it.