Man Who Could See the Truth

The Man Who Could See the Truth is a character mentioned in The Legend of Zelda: Ocarina of Time. Long prior to the events of the game, he lived in Kakariko Village. Legend has it that the man had an eye that could see the truth. By the time the events of Ocarina of Time take place however, the man is long gone and his house has been replaced with the Well of Three Features.

Theories
Although the Man Who Could See the Truth's backstory is likely only there to aid Link in completing his quest, many theories have circulated on this topic regardless.

Lens of Truth
It is probable that the Man Who Could See the Truth's eye is metaphorical for the Lens of Truth. Because the item is found in the Bottom of the Well where the man's house once stood, this seems implied. However, it is also possible that the Lens of Truth is an artifact that contains the man's actual eye which has come to be the Sheikah symbol.

Bongo Bongo
Bongo Bongo could be the Man Who Could See the Truth due to the fact that it has one eye and was living in the Well of Three Features. His house could have been sent to the Bottom of the Well, along with certain artifacts (the Lens of Truth, a Sheikah's item). His description says Phantom Shadow Beast, as "phantom" as a "dead person" and "shadow" as "Shadow Folk", another name for the Sheikah.

Existence
It is possible that the Man Who Could See the Truth never actually existed and that his story was created simply to explain the Lens of Truth's power.