We mentioned that Sega tried to make Sonic cool by giving Shadow a gun. They needn't have bothered because they already have an awesome echidna in their ranks. Knuckles looks like a red version of Sonic but he is actually an echidna, a spiny anteater who can glide through the air.
He's a complicated character, having started out as a villain in Sonic The Hedgehog 3 where he was hoodwinked by Eggman who convinced him that Sonic was planning to steal the Master Emerald. When it became clear that Eggman planned to use the Emerald to build a space station (it was pretty obvious, he attacked Knuckles in Sonic And Knuckles), the echidna joined Sonic and Tails in the battle against the villain.
Talking of Sonic And Knuckles, it was the game in which Knuckies' popularity was sealed as he was a playable character and thanks to the game's lock-on cartridge, many fans enjoyed going back to play as him in Sonic The Hedgehog 2.
He really has become an important character, reassambing shards of the shattered Master Emerald in Sonic Adventure and battling Rouge The Bat to be the first person (or rather, echidna) to find the four broken pieces of the Emerald.
You say: Before I start this I need to clarify that Sonic is obviously the best character, but as far as his supporting cast is concerned, it has to be Rad Red, Protector of Angel Island, The Guardian of the Master Emerald, or just simply Knux.
I liked Knuckles the moment he debuted as an unplayable antagonist in Sonic 3, but then he became the co-titular character for the expansion cartridge Sonic & Knuckles and that blew my 7-year-old mind. He completely opened up the scope for how you play through the levels with his awesome wall-climbing, gliding and wall smashing abilities, meaning that you could open up brand new paths through the game. He could have easily outclassed Sonic with all those extra skills, but luckily he has his own weakness in his jumping height. That meant that playing his game after playing Sonic's challenged your expectations as in some places it would be impossible to take the same route due to his limitation, leading you to discover a new way around an obstacle.
In Sonic Adventure and its sequel his personality and character were fleshed out and where other characters suffered from this, Knuckles thrived. He became this stoic and isolated figurehead of an ancient race and he was a bit more quiet which made for a nice alternative to Sonic's 'way past cool jibing'. This characterisation later got altered to a more generic and far less interesting 'all-brawn, no-brain' archetype which has been very disappointing to see for someone that genuinely admired the guy as a little kid. It's my hope then that if he does return in Sonic: Lost World he gets the same re-branding treatment that managed to make Sonic actually cool and likeable again. MartinisAwesome