Warren Buffett is widely considered to be one of the greatest investors of all time, but if you were to ask him who he thinks is the greatest investor he would probably mention one man: his teacher, Benjamin Graham. Graham was an investor and investing mentor who is generally considered to be the father of security analysis and value investing.

His ideas and methods on investing are well documented in his books, "Security Analysis" (1934), and "The Intelligent Investor" (1949), which are two of the most famous investing texts. These texts are often considered to be requisite reading material for any investor, but they aren't easy reads. Here, we'll condense Graham's main investing principles and give you a head start on understanding his winning philosophy. (For more insight, read Ten Books Every Investor Should Read and The Intelligent Investor: Benjamin Graham.)

Principle No.1: Always Invest with a Margin of Safety
Margin of safety is the principle of buying a security at a significant discount to its intrinsic value, which is thought to not only provide high-return opportunities, but also to minimize the downside risk of an investment. In simple terms, Graham's goal was to buy assets worth $1 for $0.50. He did this very, very well.

To Graham, these business assets may have been valuable because of their stable earning power or simply because of their liquid cash value. It wasn't uncommon, for example, for Graham to invest in stocks where the liquid assets on the balance sheet (net of all debt) were worth more than the total market cap of the company (also known as "net nets" to Graham followers). This means that Graham was effectively buying businesses for nothing. While he had a number of other strategies, this was the typical investment strategy for Graham. (For more on this strategy, read What Is Warren Buffett's Investing Style?)

This concept is very important for investors to note, as value investing can provide substantial profits once the market inevitably re-evaluates the stock and ups its price to fair value. It also provides protection on the downside if things don't work out as planned and the business falters. The safety net of buying an underlying business for much less than it is worth was the central theme of Graham's success. When chosen carefully, Graham found that a further decline in these undervalued stocks occurred infrequently.

While many of Graham's students succeeded using their own strategies, they all shared the main idea of the "margin of safety".

Principle No.2: Expect Volatility and Profit from It
Investing in stocks means dealing with volatility. Instead of running for the exits during times of market stress, the smart investor greets downturns as chances to find great investments. Graham illustrated this with the analogy of "Mr. Market", the imaginary business partner of each and every investor. Mr. Market offers investors a daily price quote at which he would either buy an investor out or sell his share of the business. Sometimes, he will be excited about the prospects for the business and quote a high price. At other times, he is depressed about the business's prospects and will quote a low price.