As a demonstrative: the person or thing mentioned or understood.
As a relative: who or which.
Noting a fact, reason, or result.
The ( one) specially designated.
The ( one) there.
I don't think I 'm that." – Roderick Hudson by Henry James
Isn't that so, Bobby? – The Abandoned Room by Wadsworth Camp
Look, lad, what do you think of that? – A Little Wizard by Stanley J. Weyman