Thomas "Tommy" Sullivan was an Irish man who immigrated to America, Colorado in the beginning of the 20th century along with his three sons and wife. He arrived to America when he was already forty one years of age and due to him and his family being immigrants, it was really rough for them to find worthy jobs that will be able to provide to his family.

Thomas and his wife, Akaisha had a really hard time changing jobs every short period of time and their eldest son, Adan, started looking for other ways to enlarge the income of the family. Thomas and Akaisha were both fired from their jobs and Thomas decided that if he won't do a change, the family will break apart and they will not even have enough money to live normally.
Thomas has thought to himself and he decided to begin robbing, he purchased two pistols at the black market with the small amount of cash he has had and he took Adan with him to rob.

The year was already 1920, Thomas and Adan thought together a lot about how to perform their first rob, but Adan was the brain behind all the activity.
They found paths that transportation trucks drive at that they will have very low chance to escape from the hands of the robbers.
It was December 28th, just before the new year has come and Thomas and Adan took their private and drove to the spot where they planned their robbery at.
They saw a lot of transportation trucks driving along the path that they planned but they waited for a specific truck, for a cigarettes and alcohol truck, they already knew how they look like and they spied after the trucks and wrote down their number plates for a while to make sure they will not jump on a false truck.
The moment has come and the truck that they knew that had cigarettes and alcohol inside has passed and they started pulling it over, they ambushed on it with pistols and robbed the truck and managed to escape from the place.

They successfully managed to smuggle all the content of the truck into a safe place where here came Adan's second role, to vanish the content for a good amount of cash.
Adan started making contacts in the Black Market and he successfully made everything disappear in a small amount of time and he got him and his family a wide amount of cash, amount that his family wouldn't make in normal jobs in a year.

Adan saw that this all thing works great for him thus far, so he decided to get his brothers into it and to enlarge the robberies, to rob bigger transportation trucks and make bigger cash.
A day has come and Adan and Thomas went again to rob another truck, but that black day has changed the life of the Sullivan family.
Thomas and Adan both ambushed on a truck and started the robbery, but the driver of the truck was armed himself and he returned fire towards Thomas, he killed him and Adan has managed to fire back at the driver and killed him as well.
Thomas has died in Adan's hands, and Adan knew that at this point he has no choice but to take over the family's business and to make sure he provides everything to his family.

The family was broke at this time, but Adan knew that if he will let this break the family, everything will fall apart and they will themselves in prison soon enough.
Adan and his brothers has already managed to make themselves a name and get new soldiers to their business, so Adan thought that the wisest thing to do at this point is do less dangerous things, to let the soldiers do the dangerous jobs and he will run along with his brothers the more important and less dangerous jobs.

Adan has married a woman named Alison and he brought four children with her, the eldest, Michael, Kieran, Martin and the youngest, Kevin.
Adan made sure his all sons study in school and graduate properly, he insisted that all of them will graduate successfully, out of the underworld business, but unfortunately, once Michael and Kieran who have a year difference between them, graduated, they quickly joined the business of their father and started running everything with him.
All of his sons were really wise and they helped him a lot at running the business.

Through time the organization has gotten bigger and bigger and its' leaders had more and more soldiers that worked for them.
Adan decided to start taking protection from businesses at their area, such as bars, 24/7 stores, and extort cash from them in exchange for protection from the Sullivan family.

Today the group is led by Michael Sullivan and his brothers, the children of Adan Sullivan. With most Irish-American groups being flushed out due to conflict, murder, and prison, it leaves Michael and his brothers with a bigger chance to rise. With a new structure, the group is said to have picked up where it left off, leaving all the aftermath of conflict behind them, business as usual. The spotlight has moved onto other organizations in the Los Santos underworld, giving the Sullivan Family a chance to re-evaluate future endeavors.

In recent times the figure-heads of the Sullivan Family have had their hands in various activities surrounding the criminal underworld in Los Santos. Michael Sullivan runs a tight-knit crew as of late 2019 which carries itself through both illegal and legal means. With the creation of this Los Santos outfit, it brings plenty of new conflicts along with many business opportunities.