Concise Bible Dictionary:

Roman proconsul of the province of Achaia, before whom Paul was accused; but who drove the Jews away, saying he would be no judge of words, and names, and of their law. Sosthenes was beaten before the judgment seat, but Gallio cared for none of these things (Acts 18:12,14,1712And when Gallio was the deputy of Achaia, the Jews made insurrection with one accord against Paul, and brought him to the judgment seat, (Acts 18:12)
14And when Paul was now about to open his mouth, Gallio said unto the Jews, If it were a matter of wrong or wicked lewdness, O ye Jews, reason would that I should bear with you: (Acts 18:14)
17Then all the Greeks took Sosthenes, the chief ruler of the synagogue, and beat him before the judgment seat. And Gallio cared for none of those things. (Acts 18:17)
). History states that Gallio was the brother of the philosopher Seneca, who speaks favorably of him. He was involved in the ruin of Seneca under Nero, and though he at first escaped, he afterward perished.

Strong’s Dictionary of Greek Words:

of Latin origin; Gallion (i.e. Gallio), a Roman officer
KJV Usage:

Potts’ Bible Proper Names:

Who lives on milk; giving suck; milky:―a Roman proconsul of Achaia, Acts 18:12. {Qui lactet}