It wasn't until the nineteenth and twentieth centuries, when scholars studied Rembrandt's oeuvre as a whole, that it was discovered how very many times the artist had portrayed himself. The number is still a matter of contention, but it seems he depicted himself in approximately forty to fifty extant paintings, about thirty-two etchings, and seven drawings. It is an output unique in history; most artists produce only a handful of self-portraits, if that. And why Rembrandt did this is one of the great mysteries of art history.
Most scholars up till about twenty years ago interpreted Rembrandt's remarkable series of self-portraits as a sort of visual diary, a forty-year exercise in self-examination. In a 1961 book, art historian Manuel Gasser wrote, "Over the years, Rembrandt's self-portraits increasingly became a means for gaining self-knowledge, and in the end took the form of an interior dialogue: a lonely old man communicating with himself while he painted."
quoted from Rembrandt and his Self Portraits.