Sidekick
Definition 1 of 3
Pro Tip 1/3
Not Interchangeable
Don't confuse 'sidekick' with 'partner'; sidekicks have a more supporting role. He may help a lot, but he's not my partner; he's my sidekick.
Pro Tip 2/3
Less Capable Implication
'Sidekick' sometimes implies a less skilled individual, not just a helper. I'm not just a sidekick; I solved the case too!
Pro Tip 3/3
Affectionate Tone
Though 'sidekick' can suggest inferiority, it's often used affectionately. My little brother's my sidekick; he follows me everywhere.