Prior Metal Slug
He was a former Vice Admiral in the Regular Army. In this time, he had a reputation of being a tough, efficient, and caring officer of the Regular Army, and is held in high regard by his troops. He was also a caring father to his daughter. However, Morden immediately defects over to the Rebellion when both his daughter and wife are killed in the Central Park bombing caused by an intelligence failure on the part of the Regular Army.
As he goes insane, he decides to take revenge on the Regular Army. He then creates the Rebel Army with dissidents of the Regular Army, self-promotes to a General, and starts to build up power to launch a full-scale attack. After a succession of battles, the Rebel Army outnumber the Regular Army, and earn various victories over them. The Regular Army then decides to start the production of new weapons and vehicles to turn the tables. After various tests, the SV-001 (nicknamed Metal Slug) is finally put under mass production. However, the production of the tanks is discovered by the Rebels, so they launch an attack to destroy the factories where the SV-001 is being produced and seize the finished products.
Donald Morden finally starts his coup d'état to destroy the Regular Army and conquer the world. With a grave situation on their hands (the Regular Army's), the Regular Army sends two soldiers from the Peregrine Falcons squad, Marco Rossi and Tarma Roving, with the mission to infiltrate the Rebel Army freed areas, recover the Metal Slugs or destroy them, and capture General Morden. After a bloody conflict, Morden is defeated and is imprisoned in a high-security prison.
Morden somehow manages to escape prison, and disappears from eyesight. Many rumors spread, some of them talking about UFO sightings, so the Regular Army, preoccupied to keep the secrecy in this, calls the Intelligence Agency SPARROWS, who sends two of their members, Eri Kasamoto and Fio Germi, along with the PF squad Marco and Tarma, to investigate this new uprising. Morden had made a pact with the Martians, but these aliens were just using him.
When the commandos confront Morden, the Mars People turn on him, killing his soldiers and easily destroying his saucer. Morden is levitated out of the remains of his saucer, completely baffled as a Dai-Manji beams him up. The Rebel Army temporarily sides with the Regular Army to defeat the Martians, and after a prolonged battle, the Rugname is heavily damaged. The Dai-Manji that abducted Morden explodes, and he safely returns to ground. The rebels cheer with their leader's return, with Morden being happy with the loyalty of his soldiers. Unfortunately, he was still strapped to a table and it fell, crushing him to the ground, though he still survived.
Before anything was known, the Martians kidnapped General Morden and sent a Martian disguised as him to lead the Rebel Army to build more power for a new uprising. Soon, causing strange supernatural phenomena throughout the world. Marco, Tarma, Eri and Fio once again are sent into battle. As he is defeated, he reveals himself, captures one of the Regular Army soldiers, and flees to the Rugname. Once again the Rebels and Regular Army form a temporary alliance.
After fighting their way to the command center, the player finds Morden being tortured via electrocution inside a torture room. Both Morden and the captured soldier are rescued, and the Martians are ultimately defeated. Morden is last seen in his underwear flying a commandeered Space Tank with the Rebels in Mini-UFOs, laughing triumphantly.
After a time of inactivity, the Regular Army notices a Rebel base on an open savanna, so the PF squad and SPARROWS are again sent to investigate, alongside two spec-ops soldiers Ralf Jones and Clark Still. Morden and a few Martians ride the Iron Sentinel as a means to stop the heroes. Upon its destruction, Morden and two Mars People capture the PF soldiers. However, their victory is short-lived as winged aliens suddenly appear and kill the two Mars People by eating their flesh, while Morden is dropped into the ground. He reveals that the Rebel Army and the Mars People were lifting the disabled Rootmars from the sea when strange aliens appeared and started killing the Mars People and his soldiers. A temporary alliance is made between the three groups to defeat these Invaders.
The Rebel Army, as well as Morden, have disappeared from the face of the Earth, leaving no shadows. As the SPARROWS are investigating a Cyber-Menace called the White Baby Virus, created by a group that refers to itself as the Amadeus Syndicate, a satellite camera gets a record of what seems to be General Morden using the Amadeus insignia. Without much options, PF squad and SPARROWS are sent to investigate. They find him in The Iron, an Iron Nokana-like vehicle, though it was a fake Morden who escaped via an MH-6S. Several android copies of him were also found in the communications facility.
Information about Morden surfaced after noticing in a documentary of a controversial island landfill a Rebel soldier walking on the island's shores, so the PF Squad and SPARROWS are joined once again with Ralf, Clark, and Leona to investigate. Morden is soon found in the Worm Mecha and fights them, but is defeated. Morden is revealed to have survived and is upset that he cannot do anything. Suddenly, a portal materializes and strange soldiers appear and salute him. These soldiers are actually Morden's soldiers from the future, and as a result, he starts a new uprising with them.
The PF Squad and SPARROWS eventually reach the main base. Morden is seen commanding from a Di-Cokka tank, utilizing the portal to send troops, vehicles, and launch energy spheres in an another attempt to kill them. His plans fail as the portal is destroyed, but a strange vehicle appears at the last second and Morden is dragged into it.
The Kraken is eventually confronted outside and destroyed. Morden is apprehended again, but the Mars People help him escape.
Morden continues to lead the Rebel Army, retaining his role as the Rebel Army's leader. He usually leaves the work to his subordinates Allen O'Neil and Abigail, remaining behind the scenes until someone or something gets or requires his attention.
While cornering the Professor, he was forcefully transformed into a woman. The act wounded his dignity, but he still continued to fight and he even obtained fans in the process. Fortunately, the change was only temporary and he returned to his normal self.
In the past, he was a good person. However, his personality changed greatly when his daughter and wife were killed, turning him insane. He is now a vengeful and angered person. Upon seeing the player, he often laughs in a mocking tone.
In most of the games which he appears in, he is often humiliated by either the PF soldiers or traitors, and the end result often leaves him in his boxers.
In Metal Slug Attack, Morden shows an almost equal attitude from the original game. He possesses a great interest on Orochi and " his Blood" in the Extra Ops "Blood Runaway" and informs to Abigail to find samples of the girl and the recording of the confrontation and send them to Navy for future investigation