*Reading Scholem's  historical writings along with his letters to Benjamin, we begin to understand  the depth of his reaction to the latter's leftward turn.*

Could you please clarify to me why there is an apostrophe in the word "latter". Does this mean the same as *to his (Benjamin's) latter leftward turn.* To tell the truth I am not familiar with the usage of the apostrophe in adjectives. Is it standard in English? Based on the same pattern we can write/tell: John broke the window. I am really upset by terrible's behaviour (by his bad behaviour) which is probably nonsense.