First Appearance: Episode 387 (1984)

Last Appearance: Episode 584 (1985)

Known Family: Wife - Heather O'Brien; Daughter - Katie O'Brien; Son - Jeff O'Brien (d. 1984); Brother - Jim O'Brien

Key Relationships:
Marriage to Heather O'Brien

Key Storylines:
Mike O'Brien grew up in Melbourne and went into the building industry. While working on a building site in the early-1960s, he saw an attractive girl walking past regularly, and when she sprained her ankle right next to the site one day, he went and helped her. He ended up giving the girl - Heather Townsend - a lift home and he asked her out. They later married and had two children - Katie and Jeff. The family moved from Melbourne to Perth in the early-1970s and Mike set up his own building company with his brother, Jim. Work gradually began to consume Mike, though, and he found himself working longer and longer hours. He barely saw Heather and his family and the pressure eventually became too much: Heather left him, taking the children with her to another part of Perth, where she raised them on her own.

Mike turned to his secretary, Carol, for comfort, and ended up having a fling with her. In the early-1980s, Mike's company started getting into financial difficulties. He was furious when Jim tried to save the company by putting what was left of his share of the working capital on a horse; the horse subsequently lost and Mike decided to sell-up. He reconciled with Heather, including telling her about his fling with Carol - she told him to see his secretary one more time to finish things - and they decided to move the family back to Melbourne. They returned to Albert Park - where Heather had grown up - and Mike bought up a lawnmower round.

In 1984, Jim turns up at the O'Briens', virtually penniless. Mike is reluctant to let him stay, but Heather talks him into it. Mike is furious, though, when he then discovers that Jim had helped Jeff a few months earlier when Jeff and a friend stole a car, went for a joyride and crashed the vehicle. Mike had known nothing of these events, and rages at his brother for not saying anything.

Heather's former boss in Perth, Roger Carlyle, turns up at the O'Briens', demanding to know the whereabouts of his son, Luke. Although Mike has never met Luke, the boy turns out to be the friend with whom Jeff went joyriding in Perth. Mike ends up taking Luke's side against Roger, only for Roger to take revenge by destroying Mike's lawnmowing round.

When Mike discovers that Jeff - an athlete - is being given steroids by his trainer, he's furious. He challenges Jeff and a huge row ensues. Jeff ends up running out of the house and into the street, where he's hit by a car. One of Jeff's knees is badly damaged and he's told he won't be able to run again. He turns to drink and ends up running away - although he soon returns home again. The situation is worsened when Mike learns that Jim knew about Jeff's problems and had done nothing to try and help him. Jeff eventually agrees to attend Alcoholics Anonymous meetings.

Mike is surprised - but delighted - when Patricia Morrell offers him a job working in a new company she's setting up. He begins to work increasingly-long hours, though - and also finds himself in competition with Luke: Luke is also employed by Patricia and quickly gains a promotion: Mike hates the idea of someone so young getting ahead of him and so quickly. He perseveres, though - until he meets Karen Fox, Patricia's main rival in business: she tells Mike that Luke used underhand methods to land a contract for Patricia; that Jeff passed her (Karen) information from Patricia's company; and that Luke is giving Jeff money to carry on drinking. A furious Mike challenges Patricia about the use of underhand methods - but she just shrugs that that's business and that if he doesn't like it, he can leave. Mike faces unemployment again.

Refusing to give up the booze, Jeff moves into a flat with Luke. Meanwhile, Mike and Heather head off on a holiday to try and get away from their recent problems. Unfortunately, shortly after they return events take a shocking twist: Luke is found lying dead on the floor of his flat; and a few days later, Jeff is killed in a fire at the O'Briens'. On top of all this, Katie O'Brien becomes involved with Wayne Hamilton.

A devastated Mike and Heather look for a second chance in life, and they adopt a baby boy called Jamie, not realising that he's really Beryl Palmer's baby son, Robert, who was kidnapped firstly by Gloria Dutton and then by Leigh Palmer. Mike and Heather move away to Brisbane, to make a new start - but then have to face further trauma when Beryl discovers the truth about 'Jamie' and turns up demanding her baby back. Heather refuses and Beryl eventually backs down, accepting sadly that her son has a new life. A few months later, Mike is injured in an accident on a building site, after feeling unsteady following a bout of 'flu. He appears to be making a recovery in hospital, but the doctors then discover a blood clot on his brain. They announce that it's inoperable and Mike dies towards the end of 1985.