backstabber
/ˈbæktˈsteɪbər/Definitions
1. noun
A person who betrays trust by attacking from behind, literally or figuratively.
“The politician was exposed as a backstabber who secretly worked with her opponents to undermine her colleagues.”
2. verb
To betray someone’s trust by attacking them from behind, literally or figuratively.
“The whistleblower was accused of backstabbing her former employer by releasing confidential information to the press.”