Knuckles the Echidna is one of Sonic's greatest rivals and best friends. They have known each other for a long time, but their relationship is somewhat complicated, the two of them having been summed up as "best frenemies." While Sonic exemplifies the wind and is laid-back, cool and free, Knuckles exemplifies the mountain and is stern, serious and unmovable, which cause them to argue a lot. They share a competitive rivalry and often end up fighting when clashing, although it has become less serious in recent times, being now more of a form of slapstick between the two.