Catalyst
noun, の adjective
If a mediator touches people the right way, they will become a catalyst for change. This could be good or bad change depending on what they stuck their hands in.
しょくばい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
つまり彼は二人にとって触媒のような役割を果たしたということだ。
In other words, he managed to play the role of the catalyst for those two people.