There is but one king, and I am one.
Here, the 'one' at the end of the sentence stands for 'one king' and 'one' is not specifying (in this particular place) a numeral. It is implying 'I am that one' or, more specifically 'I am that one king'.
Therefore, should 'one', when used in this way, not be considered an article with a well deserved place in the much documented sequence :
zero ... some ... a/an ... the ... null
And, if so, where in the sequence should it be inserted ?
Zero example : Who would wish to be king ?
Some example : There are some kings, it is so.
Indefinite example : I am a king and everyone knows it.
Definite example : They respect the king, thus they respect me.
Null example : Many wish to be king but the fact is that I am King.
Reference 1 : Stack Exchange - Why is 'any' not an article ?