social/mail_activity_creator/static/src/xml/activity.xml

<?xml version="1.0" encoding="UTF-8" ?>
<templates>
    <t t-extend="mail.activity_items">
        <t t-jquery="dd.mb8:first" t-operation="after">
            <dt>Creator</dt>
            <dd class="mb8">
                <img
                    t-attf-src="/web/image#{activity.creator_uid[0] >= 0 ? ('/res.users/' + activity.creator_uid[0] + '/image_small') : ''}"
                    height="18"
                    width="18"
                    class="rounded-circle mr4"
                    t-att-title="activity.creator_uid[1]"
                    t-att-alt="activity.creator_uid[1]"
                />
                <b><t t-esc="activity.creator_uid[1]" /></b>
            </dd>
        </t>
    </t>
</templates>