Wouldn't it be nice if you could simply have clients call the functions on the server without having to negotiate the connection and a protocol for the transaction? Fortunately other people have already thought about this and created the RPC (Remote Procedure Call).
Sun developed the RPC specification in 1988, but since it wasn't as platform independent as some people wanted the Object Management Group (a consortium of 700 companies which include IBM, Apple and Sun) released the Common Object Request Broker Architecture (CORBA) in 1990. Microsoft developed it's own slightly less capable version of CORBA in 1996 known as DCOM.
XML came on the scene in 1998 and prompted some to think about simplifying CORBA by re-expressing the idea of RPC as XML over HTTP. A group was formed (now the W3C XML Protocol Working Group). Dave Winer had some experience with RPC over XML, and was part of this initial working group. After some frustration with the consensus making Dave Winer released an early draft of the work as XMLRPC. SOAP v1.1 was finally released in 2000.