A fungus riding an ant, the mushroom mycologist who hands over a Holy Talisman Shard and teaches the Brainwashing Ritual.
Sozo is not really an ant. Per the wiki, the smiling mushroom on his head is a fungus piloting the body underneath, and that detail is the whole joke of the cheerful mushroom doctor who hands the Lamb one of the game's key items.
His real name is Dr. Sozonius, and he runs a tiny mushroom cult in Spore Grotto. According to the wiki he is a self-described mushroom mycologist whose followers, the Mushroomos, gather Menticide Mushrooms to feed his addiction.
He matters because of what he gives. Trading Menticide Mushrooms to Sozo earns a Holy Talisman Shard and the Brainwashing Ritual, and finishing his quest eventually turns the doctor himself into one of your followers.
This guide covers who Sozo is, his Spore Grotto quest and rewards, his three forms, how the Seed of Sozo brings him back as a follower, and what he does once he joins your cult.
Dr. Sozonius, a fungus controlling an ant and the leader of a mushroom cult.
Spore Grotto, the hidden mushroom dwelling reached during crusades.
A Holy Talisman Shard for 10 Menticide Mushrooms, then the Brainwashing Ritual for 20 more.
Plant the Seed of Sozo from his corpse to gain his follower form.Sozo, full name Dr. Sozonius, is an NPC who leads a small mushroom cult in Spore Grotto. Per the wiki his species is literally a fungus controlling an ant, with the giant smiling red mushroom on his head sitting where his brain would be.
His look matches the gag. According to the wiki he is a gray ant with red patterns under his eyes, two pairs of long arms, a yellow backpack marked with a mushroom and an X, and red mushrooms sprouting from a white beard. He calls himself a specialist in mushroom research.
He is an addict and a cult leader at once. The wiki notes his followers, the 
Mushroomos, collect Menticide Mushrooms to feed his habit, which sets up the trade at the center of his quest. For the rest of the cast, see the full Cult of the Lamb characters roster.
Sozo's quest is a two-step mushroom trade that pays out a Holy Talisman Shard and a ritual. Per the wiki, bringing him 10 Menticide Mushrooms on request earns one Holy Talisman Shard, one of the pieces of the Holy Talisman.
The second step teaches a ritual. According to the wiki, Sozo then offers to teach the Lamb the Brainwashing Ritual for 20 more Menticide Mushrooms, one of the rituals you can perform back at the cult. On completing the task he pledges his loyalty, builds a small shrine, and hands over blueprints for the Mushroom Sculpture.
Then he dies. The wiki specifies that returning to his dwelling after the quest, the Lamb finds Sozo's corpse with his head split in two and the Seed of Sozo popping out. Taking the seed and planting it is what brings him back in follower form.
Stockpile Menticide Mushrooms before visiting. Sozo wants 10 for the Holy Talisman Shard and 20 more for the Brainwashing Ritual, so 30 total clears his whole quest. In practice it is worth farming them, since the shard and the ritual are both lasting upgrades for the cult.
Sozo changes shape across his quest, and the wiki documents three forms that track his decline from mushroom guru to old ant.
The cheerful mushroom doctor with the giant smiling fungus on his head, two pairs of arms, and the yellow backpack.
His follower form after the Seed of Sozo revives him. The wiki notes his beard shrinks, he loses the extra pair of arms, and his backpack gets smaller, though the head mushroom stays.
Once he loses the giant mushroom on his head he grows old, leaving an X-shaped scar where it sat and a beard with no mushrooms left.The forms tell his story without dialogue. The fungus that made Sozo who he was is also what kept him going, so losing it ages the ant underneath into Dr. Sozonius, the man the mushroom had been steering all along.
Recruited Sozo is a quirky follower with one strong demand. Per the wiki, the first time you talk to him after resurrection he asks for 5 Menticide Mushrooms; declining simply leaves him sober.
Accepting changes him permanently. According to the wiki, feeding him brainwashes Sozo, leaving him permanently loyal in the same way as the Brainwashing Ritual. He will not do regular work, though he can still be sent on Missionary trips, and otherwise frolics around the land making noise.
He also keeps eating. The wiki warns that a brainwashed Sozo eats any fully grown Menticide Mushroom planted in the cult if you do not harvest it in time, and that he periodically gives quests to seek out unique Mushroomo followers, tying him back to the cult he used to lead.
Sozo did not arrive alone. Before the Lamb finds him, he leads his own small cult of Mushroom Followers called Mushroomos, who exist mostly to harvest Menticide Mushrooms for him.
That dynamic frames him as a darker mirror of the Lamb. He is another cult leader running another flock for his own ends, which is why his quest folds so cleanly into your cult once he pledges loyalty and starts sending you after more of his old followers.
His shrine and sculpture stick around as proof. The wiki notes the small shrine he builds and the Mushroom Sculpture blueprint he hands over, both depicting Sozo, so even after the doctor becomes a follower his likeness stays planted in the cult he joined. He sits among the wider 
cast tied to Narinder's growing congregation.
Sozo's name and title hide the punchline. Dr. "Sozo" Sozonius is a doctor of mushrooms whose entire personality is supplied by the fungus on his head, so the "specialist in mushroom research" is himself the research subject.
The Mushroomos call him "the great Sozo." The wiki lists that as one of his aliases, the reverent name his old followers use, which contrasts sharply with the addicted, mushroom-eating cultist he becomes once he joins the Lamb.
Sozo is one stop on the crusade trail. These guides cover the rituals he teaches, the cult he joins, and the Bishops at the end of the road.
Game data and screenshots adapted from cult-of-the-lamb.fandom.com, used under CC BY-SA 3.0. Original content remains the property of the wiki contributors and Massive Monster and Devolver Digital.