Characters are modelled in a neutral pose so they can be rigged and animated. Two conventions dominate.
T-pose
Arms straight out to the sides, horizontal. Legs straight, slightly apart. Facing forward.
- Easier to rig. Bones align with world axes, making placement and mirroring straightforward.
- The de facto standard for automatic tools, motion capture retargeting and engine humanoid systems.
- Worse for shoulder deformation. The shoulder is at an extreme of its range, so weights tuned there behave poorly in the middle of the range.
A-pose
Arms angled down, roughly forty-five degrees. Closer to how a body rests.
- Better shoulder deformation. The joint sits nearer the middle of its range, so skinning is accurate across more of it.
- More natural for sculpting, since the musculature is not stretched.
- Harder to rig automatically, because nothing aligns to an axis.
Which to use
If you are hand-rigging a hero character, A-pose is generally the better choice for deformation quality. If you are relying on automatic rigging, retargeting from a motion library, or an engine's humanoid system, T-pose is what those tools expect.
Why auto-rigging requires T-pose
Automatic rigging matches your mesh against an expected layout to place joints. A T-pose puts limbs in known, separated, axis-aligned positions. An A-pose moves every arm joint away from where the matcher looks, so joints land badly — most visibly at the shoulders — even though the model looks perfectly riggable.
That failure is silent rather than loud, which is why it surprises people: the rig is produced, and it is wrong.
Generating a character in T-pose
Far easier than re-posing one afterwards, because re-posing needs a rig, which is what you were trying to get. Ask for the pose in the prompt, or supply T-pose reference images.
Other conventions
Hands flat with palms down, fingers slightly spread, feet flat and parallel, head level, mouth closed and eyes open. Symmetry matters — an asymmetric neutral pose breaks mirroring.