Is there a single word for Money Lender?

Try "financier".

The Cambridge Dictionary defines it as

a person who has control of a large amount of money and can give or lend it to people or organizations

A backer is someone, or an institution, providing (usually) financial support for an undertaking. Lexico has

backer
NOUN

1 A person, institution, or country that supports someone or something, especially financially.
Which major backer would financially support a party that had no chance whatsoever of gaining political power?

Sometimes the payback isn't the usual monetary percentage, but a broader interest. For example a major engineering project such as a harbour or a railway might be supported, for the longer term goal of promoting lucrative trade.