What was the name of the person that was Arya's first kill?

Question

It was in Season 1 in the episode when Ned Stark is arrested and guards are sent to take Arya from her "dance" class. Her teacher fights them and dies, Arya escapes and doesn't go to their residence, she finds the cart that should carry their crates and her crate lay on the ground opened. Arya takes pulls out her sword, "Needle", from her crate and then someone (a child?) approaches her, Arya ends up stabbing him with her sword (Needle). He becomes the first person she kills, as far as I remember.
Do we know the name of this person?

Answer 1

We don't know; he's just called a 'stableboy'.

Throughout that scene, he's referred to as a 'stableboy' or 'the boy', and no other name is given for him:

Needle went through his leather jerkin and the white flesh of his belly and came out between his shoulder blades. The boy dropped the pitchfork and made a soft noise, something between a gasp and a sigh.
[...]
Blood had gushed from the boy's mouth as he collapsed, and more was seeping from the slit in his belly, pooling beneath his body. His palms were cut where he'd grabbed at the blade. She backed away slowly, Needle red in her hand.
[...] It would be so easy to hide here, as she had hidden from the wizard and the man with the forked beard. She could almost see the stableboy standing against the wall, his hands curled into claws with the blood still dripping from the deep gashes in his palms where Needle had cut him.
[...]
The memory made Arya smile, and after that the darkness held no more terrors for her. The stableboy was dead, she'd killed him, and if he jumped out at her she'd kill him again. She was going home. Everything would be better once she was home again, safe behind Winterfell's grey granite walls.
_{A Song of Ice and Fire, book 1: A Game of Thrones - Arya IV}

As far as I can tell, he's never mentioned again after this, and we never know his name.

In the show, she just accidentally stabs him when she's trying to get Needle out of the cart, and we learn even less about him.

See also the 'stableboy' article on the Game of Thrones wiki (which also does not know his name).

Answer 2

Game of Thrones

As per show canon we also don’t know. IMDB refers to him as “Red Keep Stableboy” so that is probably the characters official name.

The wikia on him also just refers to him as “Stableboy”.

Westeros.org also refers to the character as just "Stableboy".

Lastly, the scene happens so quickly so we never get the chance to learn his name. Here’s what the transcript has to say, again referring to him as “Stable boy”.

Arya Stark: Needle.
A stable boy appears.
Stable Boy: There she is.
Arya Stark: What do you want?
Stable Boy: I want you, wolf girl. Come here.
Arya Stark: Leave me be. My father's a lord. He'll reward you.
Stable Boy: She'll reward me, the Queen!
Arya Stark: Stay away!
Accidentally, she turns around sliding Needle through the stable boys belly. Her first kill is a fact.
Shook as she is, she runs off.
_{Game of Thrones, Season 1 Episode 8, “The Pointy End”}

---

A Song of Ice and Fire

Again per book canon we don't know, when the stableboy has a chance to introduce himself he declines.

"There she is," a voice hissed close behind her.
Startled, Arya whirled. A stableboy stood behind her, a smirk on his face, his filthy white undertunic peeking out from beneath a soiled jerkin. His boots were covered with manure, and he had a pitchfork in one hand. "Who are you?" she asked.
"She don't know me," he said, "but I knows her, oh, yes. The wolf girl."
_{A Game of Thrones, Arya IV}

Every time she remembers the event later on she refers to him as "Stableboy" too, for example.

Arya was remembering the stableboy at King's Landing. After him there'd been that guard whose throat she cut at Harrenhal, and Ser Amory's men at that holdfast by the lake. She didn't know if Weese and Chiswyck counted, or the ones who'd died on account of the weasel soup . . . all of a sudden, she felt very sad. "My father was called Ned too," she said.
_{A Storm of Swords, Arya VIII}