The furthest left efficient portfolio on the Efficient Frontier is the Global Minimum Variance (GMV) portfolio.

The minimum variance portfolio is a collection of securities that combine to minimize the price volatility of the overall portfolio.

Global Minimum Variance Portfolio: First, the variance of a minimum variance portfolio solves the last expression can be written as

The last expression can be written as

The minimum-variance portfolio with the smallest variance solves

The last equation implies

Plugging the MVP portfolio weight into the first equation results in