[DNSB]

If I remember correctly, if you look at the author(s) in the .opf file, a Kobo ereader will use the first one in the list. Quite a few ePubs I've looked at use multiple dc:creator entries for author, translator, illustrator but without adding a role or refines to specify who did what. So if the content.opf lists John P. Longland first, Kobo will use that name as the author regardless of whether John was the author, illustrator or translator.

<dc:creator>Longland, John P.</dc:creator>
<dc:creator>Michaels, Jenn</dc:creator>

Another example from the Duke Classics War and Peace is:

<dc:title>War and Peace</dc:title>
<dc:creator opf:role="aut" opf:file-as="Tolstoy, Leo &amp; Maude, Aylmer &amp; Maude, Louise Shanks">Leo Tolstoy</dc:creator>
<dc:creator opf:role="aut">Aylmer Maude</dc:creator>
<dc:creator opf:role="aut">Louise Shanks Maude</dc:creator>

Here, both the Maudes who translated the book are shown as authors but since the first dc:creator lists Leo Tolstoy, your Kobo should show that as the author. The entries for the Maudes should show the opf:role="trl" for translator.

<dc:title>War and Peace</dc:title>
<dc:creator opf:role="aut" opf:file-as="Tolstoy, Leo">Leo Tolstoy</dc:creator>
<dc:creator opf:role="trl">Aylmer Maude</dc:creator>
<dc:creator opf:role="trl">Louise Shanks Maude</dc:creator>

One of the better (i.e. less insomnia curing) pages is Readium's Parsing EPUB Metadata.

Note that these samples are for an ePub2 file, for ePub3 use role instead of opf:role.