RFC 4858 defines the role of the Document Shepherd for documents from IETF working groups, and it also says:
The Document Shepherd is usually a chair of the working group that has produced the document. In consultation with the Responsible Area Director, the chairs may instead decide to appoint the working group secretary as the responsible Document Shepherd.
Experience has shown that a successful Document Shepherd need not be the working group chair or secretary. In fact, the IESG encourages the working group chair to select an active working group participant that has strong understanding of the document content, is familiar with the document history, and is familiar with the IETF standards process. The Document Shepherd of a working group document should not be an author or editor of the document.
Not all individual submissions have a Document Shepherd other than an author or editor of the document. When there is one, the Document Shepherd is selected by the Responsible Area Director in consultation with the document authors or editors.
The Document Shepherd prepares a publication request write-up. The template for the write-up can be found here:
For working group documents:
For individual documents: