Russian Doll is one of those shows that you really feel the need to rewatch once you finish it. Netflix's strange new sci-fi drama has a lot going on with its lead character constantly dying and mysteriously resurrecting at the same party, so it is totally understandable if you missed some of the cool little changes and similarities between all the time loops. One of the wildest details that you may have missed is that one Russian Doll actor played a different character in each time loop, as BuzzFeed pointed out, and it definitely feels significant in explaining what was really going on with Nadia.
With all of the time-bending going on in Russian Doll, viewers may not have paid too close attention to some of the minor side characters, but if you did then you might have realized that many of them were played by the same guy. Actor Yoni Lotan is credited only as "Ryan" on his IMDb page for his role in Russian Doll, but it is clear that Ryan was not the same person across each of the time loops that Nadia found herself waking up in. He first appears in the series premiere as one of the three jerky men in the bodega who rudely ask Nadia for directions to a party.
A couple episodes later, we see Ryan again in a whole new capacity and with an entirely different look. Now, he is Nadia's boss at her video game coding job. And yes, the other two bosses are the other two jerky guys from the bodega. Ryan's two accomplices who seem tied to him in each time loop are unnamed characters played by Ken Beck and Max Knoblauch.
The bodega guys return in yet another form in the episode where Nadia is taken to the psych ward. The three EMTs who take her in are Ryan and his two unnamed buddies.
And finally, Ryan appears without his two friends at the end of the series, as a stranger who bumps into Nadia in the park. This time, he has two different friends alongside him.
OK, now to get into why this is such a significant Easter egg, I should first throw up a Spoiler alert: The rest of this post will deal with the season finale of Russian Doll. This Ryan guy and his two friends are the only really evident examples of a multiverse theory, where the same person will have a vastly different life in various different timelines. Everyone else that Nadia talks to in each of her time loops is pretty much the same as they were before her initial death... but then she begins to notice changes at the end of the season, like Ruth slowly becoming more cautious and people at Maxine's party gradually disappearing.
In the season finale, Nadia and her fellow time-looper Alan find that they have woken up in separate timelines for the first time, running into the versions of each other who are unaware of the time loops and about to die for the first time. Eagle-eyed viewers who may have noticed Ryan as a different person in each loop could have possibly seen this twist coming.
Another cool little detail about Ryan and the other two bodega guys is that they mention their moms in passing in each of their different iterations. This is another little Easter egg to hint that Nadia's underlying issues all stem from her relationship with her mother, which she does not fully realize until the end of the series.
Russian Doll is full of telling Easter eggs like this, and knowing about them will definitely entice fans to rewatch the show and look out for even more specifics about all Nadia's time loops.