Complex sentence: Harrington, a former Microsoft employee, founded Valve in 1996 with Gabe Newell, another former Microsoft employee: he and Newell privately funded Valve through the development of "Half-Life".
Split into simpler sentences: Harrington, a former Microsoft employee, founded Valve in 1996 with Gabe Newell, another former Microsoft employee. He and Newell privately funded Valve through the development of "Half-Life".