I own nothing. Explanation below.
"Why is there a young boy in the hall?"
"There's a boy. In the hall."
"I dunno! It's your TARDIS!"
He had traveled with Rose and the Doctor for two years. He witnessed Rose looking into the heart of the TARDIS and the Doctor's regeneration at the age of ten.
"You changed your face."
"Yeah. I did."
"You saved Rose and you changed your face."
"Does it scare you?"
"Not really. No."
"What's so funny then?"
"Rose's mum told me that she thinks that you look like you could be my dad now."
He hadn't been able to say goodbye to Rose when she first fell through the void. He could only curl up in his room and sob his heart out. He only returned to the console room because he heard a woman shouting.
"So it's not just grown women then? You kidnap little boys too?"
"He didn't kidnap me. Or you, for that matter."
"So, what? We just appeared here?"
"Well… Yeah, actually."
Donna hadn't stayed. Their next trip he remained in the TARDIS, claiming he needed a break. The Doctor had returned with a woman claiming he'd give her just one trip.
"Who are you then? To the Doctor?"
"I dunno. I guess I'm like his adopted son."
"How'd you meet him?"
"I just showed up."
Martha had kept both of them from going crazy from losing Rose. When they had run into Jack again, he had been estatic.
"It's like, I feel like you're all family. Rose was my mum, the Doctor's my dad, and Martha's my sister. You're my favorite uncle."
"And you're my favorite nephew, kid."
"I thought I told you not to call me kid! My name is Al!"
The Year That Never Was had terrified him. The Master had forced him to watch as Jack and the Doctor were tortured. He had seen far too many horrors by the time he turned thirteen.
"Al the Alchemist! Humans can't use alchemy, you know. Did the Doctor ever tell you?"
"Y-yeah. He did."
"You're just as weird as the Freak over there!"
"Jack! Y-you're killing him!"
"Isn't this fun to watch? Oh look! The lion got his head!"
Martha hadn't stayed after that. Neither had Jack. But he and the Doctor kept traveling and eventually ran into Donna again.
"Your son looks very much like you and your husband, Mrs. Noble."
"What? Oh no, he's my nephew, not my son. We're not married."
He had been so happy when Donna called him her nephew. She had understood his feelings that everyone to step foot on the TARDIS felt like his family. He was devastated when she had to leave. He met her grandfather and saw just how amazing Wilf was.
"Radiation will flood the chamber when a button is hit."
"I'll go in there Doctor. I'm an old man anyways. I'll let him out."
"No! Donna needs her grandfather! Doctor, you can do it! You'll regenerate, right? You'll survive!"
Together, they said their goodbyes, then crash landed in Amelia Pond's backyard. They told her five minutes and came back twelve years too late. He was only fourteen, younger than Amy or Rory, but he was long used to aliens when the fought Prisoner Zero.
"It's using her memories as an image, Doctor! From when she met us!"
"Then who's that between you and Amy?"
"That's you. You regenerated, remember?"
When they traveled with Amy and Rory, he tried not to be hurt when he met River.
"You don't know me?"
"Sorry, no. I have never met you before."
"But you're from the Doctor's future?"
"Then what happened to me?"
He finally understood when the Doctor was preparing to use the Pandorica for the Big Bang Two.
"I'm coming with you."
"You'll be erased from history."
"Doctor, you are my history."
He woke up in the middle of a battle field, surrounded by family and friends, as naked as the day he appeared on the TARDIS.
When Al fell through the Gate, his body ended up on the TARDIS because the Gate is the Void. He had no memories because his memories were with his soul in the armor. They called him Al because he had alchemical abilities, which humans couldn't have in the Doctor's universe (Which was why the Master called him weird). He appeared on the TARDIS shortly before the ninth Doctor regenerated. When he fell through the cracks, he was sent back to his home universe and erased from the Doctor's universe. That's why River didn't know him. Got it? Good.