His appearances in the series:
107: The One With The Blackout
116: The One With Two Parts (I)
119: The One Where The Monkey Gets Away
203: The One Where Heckles Dies
306: The One With The Flashback
Mr. Heckles lives below the apartment of the girls. In the 2.03, Mr. Heckles dies and leaves his apartment in heritage with Monica and Rachel. It was a very grumpy man and which our friends did not appreciate particularly.
Larry Hankin
He is known for his many appearances especially as a second role in series or films such as Pretty Woman.
Also, he appeared in Seinfield and Mad About You.