This formula concatenates the original value in column B to a string of asterisks (*) assembled with the REPT function so that the final result is always 12 characters:
Inside the REPT function, the text to repeat is provided as a single asterisk ("*"). The number of asterisks needed for each value is determined with with the LEN function in this bit of code here:
We start with 12, then subtract the length of the text in column B. In cell B5, "Sebastian" is 9 characters, so the result is 3. The formula is evaluated like this:
="Sebastian"&REPT("*",12-LEN(B5)) ="Sebastian"&REPT("*",12-9) ="Sebastian"&REPT("*",3) ="Sebastian"&"***" ="Sebastian***"
The results in column C is formatted with a monospaced font (Courier New) to clearly show all strings are the same length.