system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] How does a slave come by the name Skywalker?

Sounds like the name of a pilot or stellar nomad.  Was there a Skywalker clan that Shmi came from?
gpt
Shmi is the earliest Skywalker we know of. 

In Legends, her and her family were traveling in the Outer Rim, only to be captured by pirates. Whether or not they are named Skywalker is unknown.

In both Canon and legends we really have no idea about the Skywalker name. Perhaps they were from a long line of pilots and adventurers, only forgotten by time around Shmi's birth. Perhaps Shmi gave herself this last name to sound appealing to potential buyers. Maybe one of her master's gave her that last name. 

Really the point is that Shmi is the flat out beginning of the Skywalker line in many forms. And for Legends standards, she is quite under developed as a character.