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GCC was first released in 1987 when it was called the GNU C Compiler, a couple of months after it was released it was extended to support C++ too. Nowadays it supports other languages than C or C++.
Having been in use and constant development for more than 20 years it has reached a state of maturity and stability. The fact that it's so old also means that there are countless resources out there for people who want to use it.
Pro Available for even the most obscure hardware
Since it's so old and very popular it has been ported to almost any architecture imaginable. This means that it's probably compatible with even the most obscure and unheard hardware.
Pro Default on many systems
GCC is the default compiler on several systems. Most of the time people have it installed on their machine without even knowing it's there.