Demonstrative pronouns are pronouns that have a strong “pointing” component. So instead of just standing in for an entity, they point a virtual index finger at it.
Many languages distinguish between two types – pointing here and pointing “over there”.
The most common English examples are “this” and “that”.
German has “dies-” and “jen-” but it also a third “generic” type that looks like the articles. So instead of saying “this”, Germans say “the”.

Just saw this on Wikipedia on the article on DEmonstrativpronomen
“Werner war der Vater von Wolfgang. Der wurde 50 Jahre alt.
Werner war der Vater von Wolfgang. Dieser wurde 50 Jahre alt.
Werner war der Vater von Wolfgang. Jener wurde 50 Jahre alt.
Werner war der Vater von Wolfgang. Er wurde 50 Jahre alt.
In den ersten beiden Fällen ist Wolfgang gemeint, der 50 Jahre alt wurde. In den letzten beiden Fällen ist Werner gemeint.”
So apparently Der is Wolfgang and Er is Werner. I’d have felt this was ambiguous but perhaps i never was taught this. Is this true because this is new to me and it seems important?
It gives a further example that contradicts this and says its normal for this not to be followed. Is this something only a pedantic old fashioned grammatician would care about
It’s all true except the third one. I would not be sure who is the 50 year old with “jener”.
If you swap Werner for Maria, the choice between “er” and “der” stops mattering though. “der” and “dieser” are just “more pointy” than “er”, so if you use them, people would assume there’s a reason. That’s what creates the “shift” of reference in my opinion.
I think you can achieve the same in English with an emphasis.
– Werner was the father of Wolfgang and HE turned 50.
Ok, this is really interesting. I need to dive into this topic…