Comma Splice
What it looks like
Roland is a gunslinger from Gilead, he has been chasing Walter for years.
Why it's wrong
A comma can't be used to connect two independent clauses by itself. It's not strong enough. "Roland is a gunslinger from Gilead" is an independent clause. You could slap a period after Gilead, and the sentence would stand on its own. "He has been chasing Walter for years" is also an independent clause. It too would stand on its own as a sentence. When you connect two independent clauses using a comma alone, you create a run-on sentence known as a comma splice.
How to fix it
Fixing a comma splice is actually really easy. Since either side of the comma is an independent clause, we could fix the above sentence by simply swapping the comma for a period and then capitalizing the "H" in he: "Roland is a gunslinger from Gilead. He has been chasing Walter for years."
However, maybe you feel that the two clauses are more closely linked than that. Often that's the root cause for a comma splice: the author senses a relationship, but lacks the punctuation skill to accurately represent it. In that case, you can still use the comma. Just throw in a FANBOY to make the comma work. "Roland is a gunslinger from Gilead, and he has been chasing Walter for years."
Maybe the "and" feels awkward. You can always use a semicolon here, too: "Roland is a gunslinger from Gilead; he has been chasing Walter for years."
If you want to be a little more dramatic, try a dash, the "wait for it—BAM!" of punctuation: "Roland is a gunslinger from Gilead—he has been chasing Walter for years."
However, maybe you feel that the two clauses are more closely linked than that. Often that's the root cause for a comma splice: the author senses a relationship, but lacks the punctuation skill to accurately represent it. In that case, you can still use the comma. Just throw in a FANBOY to make the comma work. "Roland is a gunslinger from Gilead, and he has been chasing Walter for years."
Maybe the "and" feels awkward. You can always use a semicolon here, too: "Roland is a gunslinger from Gilead; he has been chasing Walter for years."
If you want to be a little more dramatic, try a dash, the "wait for it—BAM!" of punctuation: "Roland is a gunslinger from Gilead—he has been chasing Walter for years."