Excel Formulae: Letters In Sequence : A, B, C.....

I would like to create a column with letters from alphabet in a sequence.
If I write A and in cell below I put B then highlight the two cells and drag down I get a repetition of A and B.

How do I get the following alphabet letters ie. C,D, E etc.?

If you type the first letter into first cell (say A1), then below:

copy down ...
note once you get beyond Z you will get odd results, do you plan to go beyond Z and if so what should succeed Z ... if it is AA you can revert to an ADDRESS approach.
For example:
Say first letter was always A and was to start in A1:

copy down as far as required --
27th entry would become AA, 28th AB etc...