Charles Ellicott Commentary Genesis 26:8

"And it came to pass, when he had been there a long time, that Abimelech king of the Philistines looked out at a window, and saw, and, behold, Isaac was sporting with Rebekah his wife." — Genesis 26:8 (ASV)

Abimelech. Regarding this title of the Philistine monarchs, see Note on Genesis 21:22. As eighty years had elapsed since Abraham’s sojourn in Gerar, it is highly improbable that the same king was still reigning; but both king and people maintain on this occasion the good character they previously deserved. The Philistines, however, at this period, were a feeble colony of strangers and were kept in restraint by a sense of their weakness. They had received a vast increase in strength from abroad before they became formidable enemies of the Israelites at the end of the period of the Judges. (See Genesis 10:14.)