"Our relationship benefits us both, as he works as my employer. Though to be honest, a Yeerk can take practically full control of the host if it wants to. There was actually a war a century or so ago when the species called Andalites gave them a way to leave their planet without making sure they wouldn't decide to try to take over the whole galaxy. The Yeerks won the war, but over time factions of Yeerks decided it wasn't right to enslave people. They managed to get out from under the thumb of their government, and make a new Empire.
"In case you don't know what an Andalite is, there's one in the room. That blue mouthless herbivore over there. Weird thing is, the war is still going on for him. I don't know if we're from his furute or just an alternate dimension, but he's not overly happy with Jocun right now. Their mistake was called Seerow's Kindness, and they traveled the galaxy to wipe out the Yeerks. Of course not everything is black and white. There are good Yeerks and bad Andalites."
"By the way, Jocun is a politicion, in case you were wondering."