The name is misleading because it, they and them can be used to describe both things and people. One can also be used as a personal pronoun, and who is an interrogative personal pronoun.
There are two main forms of personal pronoun:
- subject - I, you he, she, it, we, you, they, who
- object - me, you, him, her, it, us, you, them, whom
One, they and you can also be used as impersonal forms:
- You don't often find them here.
- One doesn't need a passport for travelling in the Schengen Treaty countries.
- They say it's the best show in town.
Somewhat surprisingly, "they" can also be used as a singular form when the gender of the individual is unknown, unimportant or even when the speaker does not wish to reveal the information.
"It is I"
Some grammar "purists" maintain that after the verb "to be" the subject pronoun should be used because ... well ... they claim it should. Consequently they maintain that "It is I" is the "correct" usage.
However, if "It is I" is correct", then we should also support "It is he" and "It is she". While these may be borderline acceptable, we are then obliged to also support monstrosities such as "It is we" and "It is they" - something which nobody would want to wish on the language.
Likewise, while many people actually say "Between you and I" it is not acceptable in writing. The only correct possibility is therefore "Between you and me".
One notable difference between English and other languages is that singular and plural second person pronouns both take the same form in standard usage: "you". Several dialects have sought to create distinct plural forms, which often take the form of contractions. These include y'all ("you all"); you-uns, you'ns or yinz ("you ones"); yous, youse, or youze; you lot; you guys. 
- Trask, R. L. Mind the Gaffe (2001), ISBN 0-14-051476-7