What expressions are there for someone who likes to be alone and independent? "Lone runner" is what comes to my mind, but I don't think I've really heard it, to be honest. Could anyone help?
'Maverick' or 'lone wolf' are the words you are looking for I believe.
Maverick: an unorthodox or independent-minded person.
Lone wolf: a person who prefers to act or be alone.
Perhaps not 'lone runner', but 'lone ranger' fits the definition.
Recluse - a person who lives a solitary life and tends to avoid other people.
"He lives a reclusive life in a small island in Bahamas.
loner, lone wolf, solitary have similar meanings.