Relevant enough for Father’s Day weekend. So for the many people whose birth parent and parent through marriage are different, do you think of both equally as your parent? Or do you consider one more important than the other? Why? And do you address them differently?
For most people the circumstances would be the determining factor. I’m estranged from both my parents. They are remarried to each other after one divorce and one lengthy separation (they are both crazier than hell). My kids have a stepdad that they are very close to and haven’t spoken to their birth father in years due to abuse. They consider their stepdad to be their actual dad.
I think it would depend on your age when you get the step-parent and whether or not the original parent is still involved.
My dad married my step-mother when I was 15 or 16. She was certainly in a disticnt category from my mother (who I primarily lived with). I called her by her first name. She was seen as lesser an authoritry than either parent, and we treated eachother in a friendly, courteous manner. I certainly never gave her reason to try to exert authority over me or enact punishment. I felt I could speak freely to her as a more neutral party.
Now, to my children she is in the same category as any of their other grandparents.
Relationship trumps blood or marriage in these situations in my opinion. So whoever the kid (adult or otherwise) has the stronger relationship with should come first.
My friend told me this story recently about her stepfather, and I actually cried right there in the cafe.
Her birth father was… well, a bit rubbish. And not really around. Then her mother met this guy, and he was really nice, but just some guy. And then there was some sort of school event, and there was a stage and all the parents sitting in the audience and they kept getting these little assignments like “arrange yourselves in a line by height” - stuff like that. One of the assignments was “who has the tallest father”, and for a minute she felt really sad, realising she didn’t really have a father. Then he winked at her from the audience. And suddenly she realised that he would easily be the tallest. She took his hand and they stepped onto the stage. And then she burst into tears right there on the stage because she had a father, and he was the tallest of all the fathers, and she had a father.
And then she was crying as she told me over coffee, and then I was crying too. She took his name when she was old enough to ask. He is the man she calls papa, and I’m pretty sure he got a Father’s Day present. 
The one that is important is the one who shows up for the parenting duties.
My step-father raised me from age 4. He saw me through braces, heartache, jobs and the many problems I’ve faced as an adult. He walked me down the aisle and he is an awesome, amazing man. He IS my dad, plain and simple. And I also bore his name.
I was talking to my cousin’s 7-year-old and it took me a while to realize that his mom’s husband is “dad” and his dad is “Tim.” I kept calling his birth dad “your dad.”
His mom and dad never got married, and she married her current husband when the kid was a tot, so really that’s his dad. And Tim is a nice guy he goes with on weekends and 2 weeks in the summer.