Do you an object associated with these characters, say, are they sprite instances? Then the easiest way is to add instance variables CharName and CharHeight to the sprite. You will be able to pick a character with highest/lowest height, or iterate through them ordered by height.
If characters exist only as data, then it's a completely different approach. For example, if there is an array of characters, you can sort it by height and get the first/last record from the array.