I have started watching the Lupin III TV series and I am partway through the second series. One thing I am confused about is why Lupin refers to Zenigata as To-chan? I thought "To" meant father and "chan" was a postfix for young girls or women. What does this nickname mean, and why does Lupin use it?
Coming into this super late, but thought I may as well give you an answer.
In fact, Lupin calls Zenigata とっつぁん (tottsan), which is indeed a very rustic variation of お父さん (otou-san). This variation can very aptly be likened to "pops" in English. Just like how one might refer to the grouchy old bartender in the diner as "pops" in English, so too does Lupin (who's all-around uses very "playful" japanese) refer to the grouchy old Zenigata as とっつぁん. If I'm not mistaken, most subs will translate it to "pops" or "old man" (I'm rather partial to the former).
Hope this helps!