"(The person) to whom I owe the biggest gratitude" is the relative clause.
Relative clauses are used to attach an information onto someone or something. In other words, they tell us something in relation to a subject, hence the term "relative clause."
They are introduced by relative pronouns, such as:
- who, whom, to whom, or whose for people
- which, to which, or whose for things
- that for people or things, if you want to be less formal.
In this sentence, the clause "to whom I owe the biggest gratitude" gives an information about "my Papaw."
