Unknown CALLER.
It's got to be them.
The Big Bang Theory Season 12, Episode 23
...suggesting that he has
no personal relationship with the CALLER.
The Big Bang Theory Season 2, Episode 15
It's time for a very special guest CALLER.
The Big Bang Theory Season 8, Episode 20
...there is a gentleman CALLER
bringing flowers to your fiancée as we speak.
The Big Bang Theory Season 8, Episode 7
We have another CALLER.
Hi, you're on Fun with Flags.
The Big Bang Theory Season 9, Episode 15