A person or entity that supplies, donates, or contributes something. The specific nuance depends on context: 提供者 can be a blood donor, a service provider, a content contributor, etc.
There is a shortage of blood donors.
このサービスの提供者は大手通信会社です。
The provider of this service is a major telecommunications company.
He decided to become an organ donor.
The hospital is looking for blood donors.
The funds came from an anonymous donor.
investor; funder; financial contributor
service provider