How to create an AI character: a step-by-step guide

To create an AI character, start with one clear sentence: who they are, what they care about, and how they talk. Give them a name and a few limits. Then test them in conversation and fix what feels off. On Eternal Gardens you can draft a character from that one sentence at the Start Your Garden page, before you make an account.

This guide walks through that builder step by step, with real screenshots. Then it covers the harder part, which no form can do for you: making a character worth talking to.

What do you need to create an AI character?

You need less than you think. A good character starts with a name and one sentence that captures their role and how they behave. Everything else can grow from conversation.

Here is what most builders ask for, and why each part matters. The example is a character we made for this guide, Captain Wren.

How to create an AI character on Eternal Gardens

The start page is called "Start Your Garden." It has three short steps, and it says your draft "carries into the persona builder when you continue." It is free to start, and no credit card is needed.

Step 1: Choose a starting type

Pick the closest of four shapes. The page says you can "refine everything later."

• Myself: a character of you, in your own words.
• Someone I want to honor: built from family memories and papers, "with care."
• Fictional character or brand: for "a consistent public voice."
• Mentor or companion: a guide you can come back to.

For an invented character like Captain Wren, choose Fictional character or brand.

Step 2: Describe them in one sentence

This is the heart of it. The page says, "One clear sentence is enough." Type your sentence in the box. A tool called MemoryCraft can then "Polish with AI" if you want a fuller draft.

As you type, the page builds a starter seed. We tried it with this sentence:

Captain Wren is a retired lighthouse keeper who solves small mysteries on a foggy island and never raises her voice.

The page picked out "Captain Wren" as the working name. It set the purpose as "A creative Garden with a clear role, audience, tone, and public-safe boundaries." It also offered three first questions, such as "What tone should every reply protect?"

You can email yourself a link to the draft. The page says it keeps an unclaimed draft for 14 days.

Step 3: Save simple visual details

Write a few plain words about how the character looks. For Captain Wren we wrote about her old navy coat and her brass lantern in the fog. The portrait itself is made after you create an account.

Step 4: Create a free account and start talking

When you sign up, your start-page draft is waiting in the character builder. The quick mode asks for four things: a name, who they are (Me, Someone I love, Character or Mentor), a sentence, and a portrait. Then one button: "Create and start talking."

For the portrait you can choose stained glass, a full likeness "in jewel-tone glass," or silhouette, "a graceful outline, no face shown." You can also add a reference image or upload your own.

If you want more control, switch to the full blueprint. There you write the character's instructions. The builder's tip is to describe "voice, boundaries, style, and knowledge scope." If you're stuck, a guided interview called Eternal Guide asks gentle questions and suggests text you can use. As the builder puts it, "you can skip any question."

How do you write a good one-sentence character?

A good one-sentence character names the person, gives them a role, and adds one habit or want that shapes every reply. Vague words like "nice" or "smart" give the AI nothing to work with.

Try this pattern: name, plus role, plus what they do, plus one surprising detail.

Compare these two:

• Weak: "Wren is a friendly old sailor who likes to help."
• Strong: "Captain Wren is a retired lighthouse keeper who solves small mysteries on a foggy island and never raises her voice."

The strong one tells the AI where Wren lives and how she sounds. "Never raises her voice" will colour every answer.

There is good support for starting small. Anthropic's prompting guide for its Claude models says that setting a role "focuses Claude's behavior and tone," and adds: "Even a single sentence makes a difference."

What makes an AI character feel real?

A character feels real when it has a clear voice and clear limits, yet can still surprise you. The novelist E. M. Forster gave a useful test for this nearly a century ago.

In Aspects of the Novel, his 1927 lectures, Forster split characters into flat and round. Flat ones are "constructed round a single idea or quality." He even said "the really flat character can be expressed in one sentence." So your one-sentence draft is, by Forster's rule, a flat character. That's fine. It's a start.

The test of a round character is whether it is capable of surprising in a convincing way. If it never surprises, it is flat. If it does not convince, it is a flat pretending to be round. E. M. Forster, Aspects of the Novel, ch. 4, "People (continued)"

How do you round out an AI character? Three habits help most.

1. Explain the why. Anthropic's guide says giving the reason behind an instruction helps the model aim its answers. "Never raises her voice, because forty winters alone taught her patience" gives the AI more to work with than "calm."
2. Show, with examples. Both Google's prompt design guide and Anthropic recommend examples. Google says, "We recommend to always include few-shot examples in your prompts." Anthropic suggests three to five. Write a few short exchanges in the character's voice.
3. Set limits. Google notes that "you can tell the model what to do and not to do." Decide what your character doesn't know and what it won't discuss.

From one sentence to a short blueprint

Here is how Captain Wren could grow. Keep the first sentence, then add one line for each of these:

• The reason: forty winters alone at the light taught her patience.
• The way she speaks: short sentences, sea words and a dry joke now and then.
• The limit: she knows the island well and the mainland hardly at all, and she says so.
• The surprise: she keeps a lamp lit all night because she has never liked the dark.

The last line is what Forster meant. It doesn't break the character. It fits her once you know it, and a good chat can bring it out at the right moment.

How do you test and improve your character?

Talk to it, then edit. A short test chat shows more than an hour of planning.

Ask questions that push on the edges:

• A plain hello. Does the greeting sound like the character, or like a help desk?
• A question it shouldn't know. Does it admit that, or make something up?
• A rude or odd message. Does it stay in voice?
• A long chat. Does it drift after ten or twenty turns?
• The same question twice. Does it give the same facts?

Anthropic's guide has a useful check for written instructions: show them to a colleague with little context. "If they'd be confused, Claude will be too." Read your sentence aloud to a friend and ask them to describe the character back to you.

Fixing what you find

Most problems trace back to the sentence or the instructions. Here are the common ones.

Change one thing at a time, then run the same test messages again. That way you know which edit helped.

What about characters based on real people?

Be careful, and be clear about what the character is. Eternal Gardens describes each of its historical characters as "an Eternal Gardens interpretation" grounded in published and public-domain sources. Each one "is not the historical figure and does not speak for them."

The start page builds that care in for personal characters too. If you choose "Someone I want to honor," one of the first questions it suggests is "What should this Garden never guess or invent?" That's a good question for any character. The AI polish step is also told not to invent private facts that the user didn't supply.

Try it with a character

The fastest way to learn what works is to talk with a well-built character first. Ask the Sherlock Holmes character on Eternal Gardens to set you an original mystery, and notice how its voice holds. Our guide to Sherlock Holmes's deduction explains the reasoning it is built around.

Then go to the start page and make your own. Some first questions to ask your new character:

• What do you care about most?
• What would you never say?
• Tell me about a small problem you solved last week.
• What don't you know about?

Once your character has a voice, give it somewhere to live. Our guide to AI worldbuilding shows how to build a setting together with a character. For tips on getting honest answers from historical characters, see how to talk to historical figures with AI.