This is something which the oldies in this forum surely remember, which is missing from today's atmosphere at the Allianz Arena.
I hadn't noticed this missing only until recently when listening to some stadium chants and remembered about this guy playing his trumpet and conducting the singing. In Olympiastadion this was part and parcel of the atmosphere and I think this continued for some years in the Allianz Arena
There was one for sure called Manfred Rögelein, and I don't think there were any others.
I've researched a bit and although this guy is still cheerful, it looks like he is currently passing through some difficult times due to illness and he even ended up wheelchair bound. This guy is something of a legend in Munich and he even featured on an official FC Bayern music CD and some years ago the club paid for his hip replacement. I remember him years ago interviewed on TV programs carrying his trumpet with him and always ready to play impromptu his favourite FC Bayern tunes.
I'm sure many of you remember hearing that lonely trumpet in the background if you think about it. I wish this guy all the health that he needs.