I'm pretty sure we all heard of Birk Balthazar since the series started. Many of us were wondering if he drowned when Sofia was five. It wasn't until the series finale that we learned that theory was true. You might think he was still alive because the Narrator said that Birk was lost at sea, but Craig Gerber said that Birk was good as dead. I guess you can say "lost at sea" was Disney Junior's way of avoiding the word "died".
I guess Sofia is a lot like her daddy. He was a sailor, and she herself is great at sailing. Plus, Craig said that Sofia looks like Birk, but they don't have the same personality. I can't help but wonder what that was supposed to mean. Anyway, I kinda think that Miranda sees Sofia as a little girl version of Birk.
Also, Sofia missed her father very much. I guess in the episode "Dads and Daughters Day", when Hildegard said that Roland wasn't Sofia's real father, it made her miss her birth father even more.
I can't help but wonder what Birk's relationship with his daughter was like.