Jerry the Slime is a character in Jordan's Minecraft Survival Let's Play. He appears in episode 6, "Jerry the Slime". This episode has over 2 million views.
In the episode, he found a tiny slime in a mine and took it as his pet, and trapped him in a cage to prevent him from escaping so he could return after doing some mining, naming him Jerry. When he came back, Jerry had despawned, causing a deep sadness in CaptainSparklez. Jordan went on to name his tree after him, dubbing it 'Jerry's Tree', and placed a memorial at the top of the tree. Jerry has been mentioned frequently since. Jordan also follows a naming pattern for all his pets, with all of them rhyming with Jerry (Carrie, Mary, etc.)
Jerry also has a mod based on him, which was used in CaptainSparklez's Modded Survival series. There is also a fan game known as "The Adventures of Jerry the Slime" which CaptainSparklez played and beat.
In the next episode, Episode 7 "Mistakes were made", Captainsparklez finds another slime which he calls Ben, because he loves Ben & Jerry's ice cream, but he kills Ben soon after naming him in order to get slime balls.
CaptainSparklez: Oh hey! A mini slime! You're not gonna hurt me are you? Nope.
Captainsparklez: Ah! He's my buddy! He's my buddy. Yeah! Let's go. Let's go on an adventure man. Let's do this.
Captainsparklez: I'm gonna build you a pen, and if you despawn, so be it. But. I do not want you dyin'. You're too cute. Too cute. With your 'o' face on.
Captainsparklez: We'll need to make glass for this eventually so that people can observe your sliminess. C'mon in here. There we go. Be a good boy. See you later, don't despawn. Don't do it. Stay. My heart will be crushed. My heart will not go on if you despawn. That rhymed.
- Minecraft Survival Let's Play, Episode 6 "Jerry The Slime"