Because he's fucking hilarious and a much needed relief from all the "hand-wringing" characters on this show?

"Why does everyone keep saying, “your daughter” to Noah instead of Claire? Are they worried it’s a Bloody Mary situation, that if they say Claire enough times, Hayden Panettiere will show up on set and they’ll have to pay her?"

Ape-ceptable!

Is he going to write the script, or just insert the Flash into random scenes in Back to the Future?