Who is Jakob from A Dog's Purpose and what is their importance?

Jakob is the first handler that Ellie has as a K9 dog. His wife has died and he carries this deep sorrow in his heart which makes if difficult for him to exhibit affection. Ellie feels empathy for Jakob but doesn't like to be around such sorrow. Jakob is badly wounded during a search and rescue mission and has to retire. He goes back to school to get his law degree, meets a woman, marries her, and they have a little daughter.