What is the sender in RemoteCertificateValidationCallback?

Question

ServicePointManager.ServerCertificateValidationCallback is a property of type RemoteCertificateValidationCallback. The constructor for RemoteCertificateValidationCallback takes a delegate such as

public bool SomeCertificateErrorHandler(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
{
    return false; // Don't accept any certificates!
}

When this delegate is called, what specific type is sender? If it isn't obvious from that answer, what use is sender in this delegate?

(Just so there is no confusion, I was being facetious regarding the contents of the method. I'm interested in the parameters.)