B.D.
If he's that interested, he may want to start by reading Charles Schwab's guide to financial independence: simple solutions for busy people. It was one of the best books on investing I have ever read.
Once he has that as a foundation, I would recommend Charles B Carlson's books about Dividend Reinvestment Programs / Buying Stocks Without a Broker.
I would teach him from the beginning how to be confident in investing and eliminating unnecessary commissions.
If you go with mutual funds then Vanguard has no-load funds with low fees.