Russell "Russ" is a man that Rachel dates for one episode in The One With Russ. He looks and acts eerily similar to Ross. This freaks out everyone except Rachel and Ross, who is very jealous of him.
The fact that Rachel would date a man who resembles Ross in so many ways, even if she hasn't consciously noticed the aforementioned resemblances, suggests that she still has feelings for Ross-in other words, by dating Russ, she's really dating Ross. Monica, Chandler and Phoebe suggest this theory to her but she says that aside from similar names, she sees no similarity between Ross and Russ. She does agree that he reminds her of Bob Saget, however. Ross and Russ get into an argument at Central Perk and Rachel sees this, finally seeing how similar they really are. Clearly disturbed, she walks away.
At the end of the episode, Russ talks to Phoebe and Chandler and informs them that Rachel broke up with him. Julie enters and meets eyes with Russ.
It's worth noting that Russ apparently never mentioned what his last name was to any of the friends-which leaves open the possibility that he may, in fact, actually be a member of the Geller family, which would explain why he looks and behaves so strangely similar to Ross, if they are related. If this is true, however, they are clearly distant relatives who are unaware of each other's existence, as they didn't seem to recognize each other.
Trivia
- The only physical differences between him and Ross (aside from the clothes and a different hairstyle) are a more pronounced chin and that he appears to be slightly taller than Ross.
- His overall appearance resembles that of Fun Bobby, who appears in the same episode.