Nelson "Big Head" Bighetti, a former tenant of Erlich's incubator who works at Hooli. After work on Pied Piper commences, Big Head is offered a huge raise and promotion to help Hooli develop its copycat software, Nucleus, and leaves the incubator on poor terms with the entire team. He is later removed from the Nucleus project due to his lack of technical knowledge, and has absolutely no responsibilities at Hooli.
We have yet to learn Kyle's last name, but I'm not going out on a limb to say that's it's Bighetti. Eventually we may yet learn what it is, especially now that Kyle is dating. And thus I won't make the claim that Kyle and Nelson are twin brothers. As both series are in Earth Prime-Time, I think it's better to rely on one of the best Toobworld tropes: the Identical Cousins.
It's pozz'ble, just pozz'ble, the maiden name of Kyle's mother is Bighetti. And what helps this theory of relateeveety even more is that both Kyle and Big Head are from California.