Suspected of having something to do with his brother Harley's murder in New York
Switched Evan Whyland's medical reports after his car accident, which resulted in his death
Involved in a Salem drug ring with Stefano DiMera
Tried to kill Alice Horton, Kayla Brady, and Roman Brady
Torched Anderson Manufacturing
Stole Anna DiMera's designs
Sabotaged Anna and Tony's wedding
Torched the Salem Inn
Alex Marshall came to Salem in 1979 and worked at Anderson Manufacturing. Alex recognized Stephanie Woodruff right away as being a woman who had had plastic surgery back in New York. Alex saw Stephanie as his key to power and blackmailed her and eventually stole a Solar Power Device through Stephanie from Anderson Manufacturing. Later that year Alex Marshall set his sites on Bob Anderson's daughter Mary. In 1980 Alex married Mary Anderson in March, and soon after Mary's father died. Alex was being blackmailed by a business associate name Jarvis Maxwell, who wanted to take over Anderson Manufacturing.
After Bob died, Chris Kosnitchek was left in control of Anderson Manufacturing, and Alex convinced Chris to make him his partner. Alex also learned that Kellam Chandler was attempting a takeover of Anderson Manufacturing as well. With the help of Kellam Chandler Alex made sure that the shipment of Solar Generators Anderson was to deliver never made it to their destination. Marshall also employed David Banning to spy on Kellam Chandler for him, since Alex was still working for Jarvis Maxwell who wanted to take over Anderson as well. However, once Mary found out she kicked Marshall out of Anderson and quickly divorced him.
When Jessica Blake came to Salem Alex sponsored her tuition out of pity for the young girl, and had several arguments with Marie Horton about her, who hid the fact that Alex was her father. In 1981 Alex legally adopted Jessica Blake, and soon after Marie Horton told Alex the truth about Jessica, but made him promise not to tell her. Alex wanted to re-kindle his romance with Marie, but she refused to break her vows. Alex and Marie went on a trip to Canada to learn more about Jessica, but on the way their plane crashed. The two were forced to spend the night in a nearby cabin, and re-kindled their relationship. However, before they could make love they were rescued. Later Alex learned the plane was sabotaged and blamed Kellam Chandler. Later that year Alex eventually told Jessica that he was her father, and she accepted him, but hated Marie for giving her up and keeping Alex from knowing the truth. Alex and Marie planned to marry after Marie left her convent, but their wedding was delayed when Jessica ran off to join a convent.
Marie eventually straightened things out, but Mary Anderson would pose a threat to Alex and Marie's relationship. Mary still wanted Alex back, so she tried every trick in the book to make Marie think Alex was having an affair with her, and Marie eventually fell for it. Marie left Alex, and shortly after Alex was shot, and David Banning was arrested when he was seen by Renee Dumonde holding the gun. Alex fell into a coma, and when he awoke he had no memory of who shot him and he was paralyzed from the waist down. Marie moved back in to take care of Alex, but would not sleep with him, or marry him just yet. Later Marie and Alex eventually parted.
While at the hospital for a check up Alex saw the man who shot him coming from Stuart Whyland's office. Alex confronted Stuart, and he blackmailed Alex into helping him takeover Anderson Manufacturing. Stuart demanded Alex say that David shot him, but Alex did no such thing. Stuart feared for his life, and quickly left Salem. Alex Marshall soon became involved in a drug ring, and with Stefano DiMera. Stefano was being blackmailed by Evan Whyland, and ordered Alex to take care of Evan. Alex switched Evan's medical charts before he was set for surgery, and as a result Evan was given some penicillin which killed him.
Later Alex and Stefano's drug ring would be infiltrated by Roman Brady, and they both vowed to have revenge on him. Alex tried to punish Roman by killing Kayla with a robot which had a poison needle. Kayla fell into a coma but survived. Later Alex tried to kill Alice Horton, but killed a nurse by mistake. At Roman's wedding to Marlena in 1983 Alex tried to have Roman killed, but failed. When Stefano died in 1983 he left a 2 wills, but the second will was known only to Alex at the time. In the second will Renee Dumonde was left a substantial amount of money, so when she divorced from David Banning, Alex quickly married her. The marriage was short lived, because a week or two later Renee was murdered by the Salem Slasher.
When Anna DiMera found incriminating evidence that implicated Alex in dealings with Stefano Alex went after her, but she managed to get out of town in time. Later, the evidence connecting Alex to Stefano was destroyed, and Anna returned safely to Salem. Alex however managed to get Anna to spy on Tony DiMera for him. Alex donated 1 million dollars to the hospital in the spring of 1984 during a charity event for the new psychiatric wing of the hospital, knowing that Stefano had rigged a bomb to go off at the theater where the event was taking place.
In 1984 Alex faced a financial crisis, much of his money was missing from his Swiss bank accounts and shares of Anderson were being bought up at an alarming rate. In order to save his financial savings Alex opened up a fashion company with Anna DiMera, which he later sold. Through the encouragement of Linda, Alex set fire and destroyed Anderson Manufacturing, hoping to collect insurance on it. Later the two were found out by Larry Welch, and he blackmailed them. In 1985 Alex stole his ex wife Anna's dress designs, but Anna had the last laugh when Eugene rigged the fabric on the dresses to disintegrate while they were on the runway. When Anna and Tony tried to get married Alex thwarted their plans by replacing the minister with an actor.
Later that year Alex helped Victor Kiriakis buy up large portions of the businesses in Salem. In 1986 Alex married Emma Donovan, but she was murdered in 1987. Shortly after her murder was solved, Alex was sent to prison for burning down the Salem Inn to collect the insurance money in 1987.