As I mentioned over in my MarioSonicGames.com blog yesterday, this year is the 30th Anniversary of Mario, and the 20th Anniversary of Sonic.
The first ever Mario game, the original Donkey Kong arcade game, appeared in 1981. Although the hero character of that game was originally known as Jumpman, he quickly became known by his now world famous name instead, and since then Mario has appeared in over 200 different games.
The first ever Sonic the Hedgehog game appeared on June 23, 1991 on the Sega Genesis/Mega Drive 16-bit games console, and a few months later on Sega's Master System and Game Gear 8-bit games consoles as well.
Over the years since their creation they have become the two best-known video game characters in the world.