Why is the 4G63T called the Evo engine?

The 4G63T 2.0L turbocharged inline-four powered the Mitsubishi Lancer Evolution I through Evo IX (1992-2007). During this 15-year run, it won four consecutive WRC Drivers' Championships (Tommi Mäkinen, 1996-1999) and established Mitsubishi as a rally racing powerhouse. The Evo X switched to the aluminum 4B11T engine in 2008.