Knuckles the Echidna...he mainly guards the Master Emerald on Angel Island so he doesn't leave much but when after a bit...he trusts you around it and him but he's always there to help and you wanted to hang out with him to at least try to get him out.

Knuckles the Echidna: "For the last time. No. I can't leave the Master Emerald after Neo Metal Sonic took over my Island and after Eggman stole the Master Emerald I can't risk losing it anymore."