Dear Miss W____:
>>I have always believed that the following sentence should be written like this:
>>Lt. Worf, although large, has not got a head like Rikers.
>>However my word processor is telling me it should be as so:
>>Lt. Worf, although large, has not got a head like Riker’s.
>>Could you verify for me which is the correct way of writing this sentence?
The second sentence is correct. Adding an -s to most words make them plural. Adding an -‘s to most words makes them possessive. The second sentence tells us that the head belongs to Riker. The first sentence means the head does not look like the head that most Rikers have. That would work, for example, if Rikers were a group instead of an individual. “Seven of Nine does not have head markings like Klingons.” In your example, though, you are speaking of the head that belongs to someone named Riker and there is only one Riker, so this is clearly possessive and not plural.