The end of Guardians of the Galaxy sets up the mystery of Star-Lord's dad, an unknown character who is not actually human. Comic fans know who Quill's dad is in the books - J'Son, King of Spartax. But don't expect that to be the answer in Guardians 2.
"It’s definitely not the character who it is in the comics, I’ll say that much."
So who is it? I've speculated here, and Gunn adds some hints:
"There have been a lot of documents passed around about who Peter Quill’s father is between a select two or three of us. That’s been part of the plan since the beginning, that’s something I had to work out before we shot the screenplay. We wanted to make sure Yondu’s place in everything made sense and it does, so it’s all very specific stuff."
Which raises the question of 'what is Yondu's place?' In the comics Yondu lives in the 31st century - will Guardians 2 reveal that there's a time travel element to all of this, and that Quill's dad comes from the future?
Meanwhile, Gunn says to not expect much from Thanos in Guardians 2.
"He will show up [in the sequel] if he helps our story and he will not show up at all if not. Thanos is not the most important thing in Guardians 2, that’s for damn sure. There’s the Guardians themselves and other threats the Guardians are going to be facing that are not Thanos."
And so Thanos' run as the least interesting Big Bad ever will continue...