Predecessor or precursor
I was happier with this president's predecessor.
President Obama's predecessor was George W. Bush.My predecessor appointed me presidency last year because of my avid appreciation for Japanese culture.
The new governor found it necessary to change some of the unfair policies implemented by his predecessor.
The Greek word idiotes is the ancient predecessor to idiot.
The phonograph was the predecessor of the gramophone.
The opposite of an ancestor would be a descendant.(Your ancestors are your progenitors, while your offspring and their offspring are your descendants.)The opposite of an ancestor may also be known as a successor. However, this is the direct opposite of predecessor.
what word is opposite of prudent
The opposite of anything is it's absence. Silence would be the opposite of a word spoken.