A Common Misconception About 'That'
Related to, but not the same as, this week's podcast, here's a helpful fact about "that" and "who." A lot of people believe that you can't use "that" to refer to people: "There's the man that I was telling you about." People, these people will tell you, take "who."
If you look up "that" in the dictionary and read through its many, many definitions, you'll see that "that" can sometimes be used as a synonym of "who," making "the man that I was telling you about" grammatically correct.
But is it a good choice? That's another question entirely. In copy editing, we like to use the most precise words possible. If it's true that "that" can mean a person or a thing, "who" is the better choice for people because it can only mean one of those. It's more specific. But that's a preference, not a rule.