Hester visited Seattle on Wednesday but chose to return to the team that moved up to draft him in the third round in 2008.
Free-agent quarterback Charlie Whitehurst, who was traded by the Chargers to the Seattle Seahawks in 2010, also re-upped with the Chargers this offseason, opting for sunny Southern California rather than the rain-drenched Pacific Northwest.
And whereas many teams in the NFL are phasing out the fullback position, the Chargers have added two this offseason. Last month, the team signed free agent Le'Ron McClain, who is expected to be the starting fullback. Hester will likely play extensively on special teams.
Since he joined the team, Hester has played 62 of 64 regular-season games with 23 starts.
Henderson has appeared in 44 games and started 28 between 2007 and 2010. He saw his most significant action in 2009, starting 16 games on the left side. Listed at 6-foot-7 and 300 pounds, Henderson was out of the NFL last season after reportedly arriving at Raiders camp out of shape. He kept active by playing for the Colorado Ice of the Indoor Football League.
The Chargers have been busy this offseason, signing 16 free agents since March 13. Only four of the acquisitions play defense.