Get a related entries author in a plugin
Something like this should do it:

// Grab an entry.
$entry = craft()-&gt;entries-&gt;getEntryById(4);

// The current entry's author.
$originalAuthor = $entry-&gt;getAuthor();

// This is assuming your Entries field is called "relatedEntry"
$relatedEntry = $entry-&gt;relatedEntry-&gt;first();

// Make sure one was selected.
if ($relatedEntry)
{
    // The related entry's author.
    $relatedEntryAuthor = $relatedEntry-&gt;getAuthor();
}