THAN 
conjunction
1.
(used, as after comparative adjectives and adverbs, to introduce the second member of an unequal comparison):
She's taller than I am.
2.
(used after some adverbs and adjectives expressing choice or diversity, such as other, otherwise, else, anywhere, or different, to introduce an alternative or denote a difference in kind, place, style, identity, etc.):
I had no choice other than that. You won't find such freedom anywhere else than in this country.
3.
(used to introduce the rejected choice in expressions of preference):
I'd rather walk than drive there.
4.
except; other than:
We had no choice than to return home.
5.
when:
We had barely arrived than we had to leave again.
preposition
6.
in relation to; by comparison with (usually followed by a pronoun in the objective case):
He is a person than whom I can imagine no one more courteous.
Origin
Old English

Idioms and Phrases with than
than

actions speak louder than words
bark is worse than one's bite
better late than never      más vale tarde que nunca
better safe than sorry
better than
bite off more than one can chew
blood is thicker than water
easier said than done
eyes are bigger than one's stomach
in (less than) no time
less than
more dead than alive
more fun than a barrel of monkeys
more in sorrow than in anger
more than one bargained for
more than one way to skin a cat
none other than
no sooner said than done

5. We had barely arrived, then we had to leave again.

6. He is a person than whom I can imagine no one more courteous. - I think something is missing here. Maybe "I can't imagine a person more courteous than him."

Thank you,I learned something new.

Thank you both of you for your comments. We all get a little relaxed in our first language and are capable of writing simple grammar errors because words like your and you're sound the same. I am a writer and I do the same.

And thank you for the correction on than being a preposition and conjunction.

Than

is a conjunction,and a preposition.