First convention officially named San Diego Comic-Con. The convention that was to become Comic-Con started in 1970 and was called the Golden State Comic-Minicon, but in 1973 the convention officially changed its name to the San Diego Comic-Con and expanded to 5 days.
And please, PLEASE check out the pictures from that 1973 convention. They are eerily familiar. Most of the elements from today's convention have their seeds back then.