Step 1: Create a game starring your character that revitalizes the game industry.
Step 2: Slowly update your character design through decades of iteration
Step 3: Place that character as the star of nearly every major launch title game for the new consoles you release
Step 4: Then place that character in dozens of various game genres like golfing, basketball, tennis, kart racing, rpgs, soccer, baseball, etc.
Step 5: Market that character tirelessly. Make cartoons starring the character... t-shirts, hats, backpacks, toys, posters, stickers, cereal, lunchboxes, bad live action movies, etc.
Boom, your character is more recognizable than Mickey Mouse. (no joke)
Also some additional tips:
- The character should either not talk at all, or be super positive with almost a naive child-like quality about them. The child-like aspect works well to reach a massive audience and helps make the character endearing and likable. (Mario, Link (the non-animated series versions), Mickey Mouse, Spongebob, Pikachu, etc) Conversely, you could give them some "attitude" but this tends to limit your audience down to mostly boys or younger people only (Sonic, Conker, Donkey Kong, Link (the animated series version), Ratchet & Clank, Crash Bandicoot, Earthworm Jim, etc)
Note that the more attitude you give the character, the less likely they are to reach "Mario" status. The more extreme you push one aspect of a character's personality, the more you isolate the audience.
I feel like this is why Sony has never had a breakout mascot that really represented the company throughout the years. Pretty much all their characters have serious 'tude, and it causes a disconnect with a lot of people. I guess Spyro is like a halfway between Mario and a 'tude character, which is why he's been mildly successful but still hurting because they give him the stupid eyebrows:
("Look at this raised eyebrow! DO YOU SEE HOW MUCH ATTITUDE I HAVE?!")
Oh, if you want your character design to never reach mass popularity, give them the stupid raised eyebrow as their signature look. Guaranteed to stay mediocre.
Also sunglasses... stay away from sunglasses...
(Even generic dino side-kick disapproves)
In fact, stay away from any clothing that is currently "in". Plenty of early 90's characters with the backwards hats and jeans and sneakers and sunglasses who are now just jokes.