His previous alias, "The Sentinel's Sorrow", was replaced by "The Colossus" after his Champion Update.
He references his previous alias while attacking a Blue Sentinel: "You're a sentinel? I'm a sentinel! We should fight!"
In this case however, this interaction has literal implications: Galio being a textbook-definition sentinel for Demacia, and Galio perhaps sharing similar origins with the Blue Sentinel, both being rock/mineral beings empowered/given life by magic.
Galio is seemingly short for Galileo, after the Renaissance Pisan polymath.
The name means "man of Galilee", ultimately from Semitic root g-l "circle."
"I came to chew bubblegun and kick butt, and I'm all out of butt." is a reference to the 1988 film They Live in which the main character, enters a bank with a pump-action shotgun and says "I have come here to chew bubblegum and kick ass, and I'm all out of bubblegum."
It is also a reference Duke Nukem with the quote "It's time to kick ass and chew bubblegum, and I'm all out of gum."
The quote "From the frozen loom!" upon buying Glacial Shroud is a reference to the famous quote "For the Frozen Throne!" spoken by numerous characters in WarCraft III.
It is uncertain how long ago Durand created Galio.
Considering he and Poppy know each other, he is at most as old/older as/than the Kingdom of Demacia ever since its founding by Orlon himself.
And given he and Sion fought each other many times back when the Undead Juggernaut was alive, Galio (and by extension Durand) is at least a contemporary or Jarvan I's.
Galio sees Lux as the only mage he likes, and has become a sort of Guardian to her.