Gunther

Gunther is the manager of the Central Perk coffee house, who first appears as a background character in "The One with the Thumb". This character develops an unrequited crush on Rachel in the third season, which he keeps to himself until "The Last One". His jealousy of Ross is made clear numerous times, most notably in "The One the Morning After", when he reveals to Rachel that Ross cheated on her when they were "on a break".

ROSS: Gunther! Gunther. Gunther, please tell me you didn’t say anything to Rachel about me and the girl from the Xerox place.
GUNTHER: I’m sorry. Was I not supposed to?

Son of a bi... well... let's move on...
Gunther appears in nearly every episode, but only occasionally calls attention to himself and almost never has a large role in the plot of an episode. In the Season 8 Episode 'The One With The Stain', Gunther is shown to be fluent in Dutch, calling Ross an "ezel" as he converses with him. Ezel means something like "monkey".



Anyway, Gunther is hilarious, and is not so unusual to be in love with Rachel.