Ich verdanke das, was ich heute bin, meinem Vater.
I believe “se … debo” stems from “deberse”.
“Lo que soy se lo debo a …” as I currently understand it would then mean something like “That which I am is due to …” (I could be wrong though).
How do you understand this sentence?
No, this is actually le + lo becoming se lo.
Thank you for the feedback! Could both points be true? Or, asked differently, why is “le” necessary?
Could it be that “deber” combined with a pronoun (“le” in this case) means “to be due to”? This is the point I wanted to make. To express the meaning of this sentence, you need to add a pronoun to “deber”.
But, as you say, “le” combined with “lo” makes “le” change to “se”.
Thanks for helping out a beginner. 
I think you should rephrase the question as “why is le used”? My non-native answer is that it’s not necessary but it’s idiomatic. To understand this sentence, you need to know that one basic meaning of deber is “to owe”: “I owe it to my father what I am today”.
If it would stem from “deberse”, wouldn’t it become “me lo debo a mi padre”?
Theoretically, yes, but deberse is only used impersonally, and it doesn’t take an object.
