The latest chapter revealed that Shimotsuki Ushimaru was a member of the Shimotsuki Family, and the last daimyo of Ringo in Wano Country. He ruled until the takeover of Kurozumi Orochi as shogun 20 years ago.
I noticed right away that he bears resemblance to Zoro, which leads me to believe that he is his father.
20 years ago, Kurozumi Orochi assumed the title of shogun, and after executing the daimyo of Kuri Kozuki Oden, he gave the remaining four daimyo the chance to submit to him. The daimyo all refused and staged a rebellion against him. The rebellion was quashed by Kaido, resulting in Ushimaru losing his life.
Zoro at this time would’ve been 1 years old, and having lost his parent(s) would’ve probably been evacuated from the island to safety. We already know that a ship from Wano traveled to the East Blue and I suspect Zoro was on this ship. These people of Wano created Shimotsuki Village in the East Blue in order to honor their fallen daimyo, and thus Zoro was never told about his family.
The two most prominent families in Wano that we have seen have been the Kozuki and the Skimotsuki.
So I think it will be Momonosuke and Zoro that will bring peace back to Wano and finally open its borders. This would also add context to the brotherly bond these two share as Zoro has been shown to be teaching Momonosuke sword techniques.
*Theory by cwahsonenthusiast