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. Although he has frequently noted the similarities in appearance between Ushimaru and Zoro, Oda confirmed in the SBS that Ushimaru is not Zoro’s father. You can read them below:

Question: Lord Oda Eiichiro, I have read chapter 1024 and is deeply intrigued. Is the person who call himself “so and so” the father of Mr. Zoro?

Oda: I got a lot of questions about “so and so”. It’s kind of rude to reveal it since the person we’re talking decide to hide it, but since a lot of you are asking I’ll formally introduce them.

Daimyo of Ringo: Shimotsuki Ushimaru

Daimyo of Kibi: Fugetsu Omusibi (triangle head person)

Daimyo of Udon: Uzuki Tenpura

After the death of Oden, all of the regions rise up to take down Orochi, but they were defeated by the Beasts Pirates. Shimotsuki Ushimaru and Onimaru, the fox who stole shusui from Zoro, was a famous duo. There was originally going to be a scene when Onimaru is stealing Shusui, he is shocked by the appearance of Zoro, who looks identical to young Ushimaru; but that just makes things complicated so it got cut, besides it might not even be brought up in the manga.

Anyway I’ll answer your question, Ushimaru is not Zoro’s dad. These three characters’ name won’t be revealed in the manga, so I include them here. Regarding the lineage of Ushimaru, I’m not sure whether I’ll draw more or hide it, so let’s end the discussion here. They really do look alike huh?