Here you go:
https://www.dictionary.com/browse/white-knight
This is my personal favorite, though:
https://www.urbandictionary.com/defi...White%20Knight
White Knight
A person with low self esteem who combats this with a unwavering need to aid others who may or may not need it. They usually have very isolated personal lives as they are very judgmental of others, surrounding themselves only with those who feed their desire to help and feel as a savior. Most commonly sighted in young men in regards to women, this is only a lesser form as it is usually only temporary, fading with life experience. More serious cases occur in correlation with chronic self esteem problems where the person needs to maintain a high view of themselves through self righteous acts of kindness. These people enjoy surrounding themselves with troubled individuals, who form a farm which is harvested for what they use as pseudo self esteem.
