Re- Dovid Hamelech,
There was actually a joke made by a shadchan who wanted to red a shidduch from a simple family to well known people who stemmed from a famous , illustrious Rav of the 19th century .That rav had a yichus briev which traced back to Dovid Hamelech.
When the shadchan suggested the idea, the matriarch of the famous family snubbed it by saying that they would never take such commoners when their famous ancestor can trace back to King David.
The shadchan replied, ‘ Dovid Hamelech was a self made Yichus, he stemmed from Geirim, which means you do to!’