Donald makes his first appearance in Emmerdale when he is on life support in hospital after a brain haemorrhage. His second wife, Nicola Blackstock, returns to Emmerdale, claiming to be a widow. Jasmine Thomas an aspiring local journalist, is annoyed that Nicola is flirting with her boyfriend, David Metcalfe, and discovers that Donald is in a coma in hospital. In late December, Donald regains consciousness and is aware that Nicola only married him for his money.
When Donald's alcoholic son Miles - who Jasmine had tracked down - discovers Nicola's affair with David, he tells Donald, who demands a divorce. However, Nicola agrees to end the affair and he comes home from hospital, moving into Holdgate Farm. He hires an actress, Cindy, as his "nurse", annoying Nicola, who tries to murder Donald repeatedly, hoping people will blame Cindy. David ends his relationship with Nicola when Donald offers him a position in the business, and tells him about Nicola's attempts to kill him. However, he takes her for a picnic on the moors and confronts her, giving her the opportunity to push him off a cliff. He even taunts her by pushing his wheelchair near the cliff edge and almost falls. Nicola can't do it, however, so they return to the village and he throws her out but refuses to tell the police about her behaviour. The subsequent divorce battle sees Nicola try to get as big a settlement as she can. His final offer is £20,000, which she accepts days before his death.
A successful businessman, Donald's company, "De Souza Enterprises", takes over the refuse collection contract from the Kings and persuades Carl King to join him. Miles, after numerous arguments with his father and ending his relationship with Jasmine, leaves the village in August 2008.
In July, Donald's daughter Anna arrives in the village, having lived in Dubai for years after arguing over a man Anna was in love with. However, they reconcile and she gets a position in the company - coming into conflict with Carl. Carl later betrays the De Souzas when he gives a contract to his brothers. Donald then buys Carl out and determined to get revenge, Donald and Anna agree on a plan - she will ingrain herself with the Kings so she can get the details on important contracts and steal it. However, she finds herself falling in love with Carl's brother Matthew, and cannot betray him as planned. Donald is furious about this and attempts to break them up. When Matthew and Anna get engaged, they have a dinner party to celebrate. Hoping to make amends, Anna invites Donald - but he is disruptive, saying Anna only wants Matthew for his money. After he leaves, Matthew visits Donald at Holdgate Farm and during a heated argument, Donald has a heart attack. Matthew withholds Donald's pills until he agrees to come to the wedding and put Anna back in his will, but Donald dies due to Matthew not giving him the medication.
"You are not Christine.'' (First line)
"Please, my pills! Ambulance! Ambulance, now! PLEASE!" - To Matthew whilst having a heart attack, just before the attack kills him