The Abu Sayyaf Islamic militant group has terrorized the Mindanao region and nearby areas with a trail of bombings, kidnappings and beheadings since the 1990s.
Filipino and Canadian officials said Tuesday the group had murdered Canadian retiree John Ridsdel, seven months after abducting him along with two other Westerners and a Filipina at a southern resort.
The following is a timeline of the Abu Sayyaf's rise and rampage:
Early 1990s: Libya-trained preacher Abdurajak Janjalani forms the Abu Sayyaf (Bearer of the Sword) with young Moros disaffected by an older generation of guerrillas.
The new group is backed by seed money from a local charity run by Mohammad Jamal Khalifa, a brother-in-law of al-Qaeda chief Osama bin Laden.
April 4, 1995: Hundreds of its gunmen sack the southern town of Ipil, leaving more than 50 people dead.
December 18, 1998: Janjalani is killed in a clash with security forces on the island of Basilan and is replaced by younger brother, Khadaffy Janjalani, who is killed in September 2006.
April 23, 2000: The group makes its first known foreign sortie, snatching 10 Western tourists and 11 Asians from island resort of Sipadan off Malaysian Borneo.
The hostages are freed in August 2001, with the Westerners flown to Tripoli aboard a jet sent by then Libyan leader Moamer Kadhafi, who is said to have paid millions of dollars in ransom.
May 27, 2001: Three Americans are among 20 people snatched from a western Philippine island resort. One of them, tourist Guillermo Sobero, is beheaded 13 months later. Most of the local hostages are ransomed off.
One of the other Americans, Christian missionary Martin Burnham, and a Filipina hostage are killed in a military operation in June 2002. But Burnham's wife is rescued.
February 27, 2004: The Abu Sayyaf firebombs a ferry in Manila Bay, killing 116 people in the country's deadliest terrorist attack.
July 10, 2007: The Abu Sayyaf and fighters from the mainstream guerrilla group Moro Islamic Liberation Front kill 14 Filipino marines on Basilan, beheading 10 of them.
December 5, 2011: The Abu Sayyaf abducts Australian ex-soldier Warren Rodwell at his southern Philippine home. He is freed unharmed in March 2013 after a reported ransom of nearly $100,000 is paid.
February 1, 2012: Two bird watchers, a Dutchman and a Swiss, are abducted in the Tawi-Tawi island group. The Swiss man escapes in December 2014.
April 25, 2014: German couple Stefan Okonek and Henrike Dielen are abducted from a yacht off the western island of Palawan. The couple are ransomed off six months later.
Sometime in mid-2014: Isnilon Hapilon, who has a $5-million bounty on his head from the US government, becomes the first of several senior Abu Sayyaf leaders to pledge allegiance to Islamic State.
May 14, 2015: Malaysian tourist Bernard Then and restaurant manager Thien Nyuk Fun are seized in the Malaysian port of Sandakan.
The woman is released in November, reportedly after a ransom was paid, but the man is beheaded.
September 21, 2015: Canadian tourists John Ridsdel and Robert Hall, Norwegian resort manager Kjartan Sekkingstad, and Hall's Filipina girlfriend are seized from yachts docked at a resort on Samal island, hundreds of kilometres from Abu Sayyaf strongholds.
The kidnappers later threaten to behead one of the hostages if ransom is not paid by April 25.
October 7, 2015: Retired Italian priest Rolando Del Torchio is kidnapped at his pizza restaurant in the southern city of Dipolog, also far from Abu Sayyaf strongholds. He is freed unharmed on April 9 this year.
March 26, 2016: Ten Indonesian sailors are seized from their tugboat off Malaysian Borneo. The vessel's owners say the Abu Sayyaf demanded a ransom.
April 1, 2016: Gunmen on speedboats seize four Malaysians from the east coast of Sabah state. Malaysian authorities describe the gunmen as Filipino.
April 16, 2016: Gunmen abduct four Indonesian sailors on the high seas off Sabah. The Philippine Army suspects the Abu Sayyaf to be behind the kidnapping.
April 25, 2016: A decapitated human head turns up on Jolo island, an Abu Sayyaf base, as Canadian Prime Minister Justin Trudeau denounces the "terrorist" murder of Ridsdel, one of the hostages held in the Philippines.
— Agence France-Presse