Fill a column with a character.

Hello
This should be easy but I have been struggling with it. I have a file with 4 columns. The fifth column needs to have a character typed in it. My CAD program won't except the data file without a character in it. I know how to copy and paste but the problem is ..... There needs to be an entry for 1048000 rows. It took my PC 45 minutes to scroll the length of the column the last time I shaded the cells I needed to paste into. Is there a way to tell excel to copy the character "x" from E1 to E2 to E1048000 instead of dragging down the entire column? I tried using Ctrl-End command which instantly takes me to the end of the column but I don't know how to use it in conjunction with my copy and paste commands. Thanks for any advice.

Or just as another option

with E1 selected and the value entered in it.

Ctrl+shift+down
Ctrl+d

(I guess you don't care if it goes to 1048576 instead of 1048000 its just a matter of having data in more cells than you could possibly use)