reliever
1. [ noun ] a person who reduces the intensity (e.g., of fears) and calms and pacifies
Synonyms: comforter allayer
Examples:

"a reliever of anxiety" "an allayer of fears"

Related terms: person comfort
2. [ noun ] someone who takes the place of another (as when things get dangerous or difficult)
Synonyms: relief fill-in backup backup_man substitute stand-in
Examples:

"the star had a stand-in for dangerous scenes" "we need extra employees for summer fill-ins"

Related terms: peer surrogate locum_tenens double substitute
3. [ noun ] (baseball,sport,softball,games) a pitcher who does not start the game
Synonyms: fireman relief_pitcher
Related terms: pitcher closer take_over