If -
Halo is 0.5
Soy is cunning
Pot is a dab
Rio is free
Oil is 0
Lost is an ultimate
Bio is substantial
Then,
My favorite Lord of The Rings character is ?
Let's replace the right sides with synonyms that match the left side when one letter is replaced by the One Ring - er, I mean an 'O':
Halo is 0.5 - halo is halF.
Soy is cunning - soy is sLy.
Pot is a dab - pot is pAt.
Rio is free - rio is riD.
Oil is 0 - oil is Nil.
Lost is an ultimate - lost is lAst.
Bio is substantial - bio is biG.
The letters replaced by O are FLADNAG... Which, backwards, reads GANDALF! A great character indeed.
* cleaned up this post per notes by op, tech, and IIC.