The phrase "key backer" refers to an important supporter or sponsor of someone or something. They provide crucial financial, emotional, or other forms of assistance to help that person or thing succeed. Full definition
I'm actually more worried that key backers of school choice are starting to abandon private school choice and focus all of their energies on charters. (educationnext.org)
Key backer Benchmark Capital sues Kalanick over allocation of board seats. (fortune.com)
Niou, who works for Queens Assemblyman Ron Kim, has garnered several key backers, including influential labor unions 32BJ and the United Federation of Teachers. (nydailynews.com)