Martin McGuinness, an important politician in Northern Ireland, has died at the age of 66 due to an illness.
As a member of the political party Sinn Fein, he was deputy first minister of the country from 2007 to 2017.
He is an important character in the recent history of Northern Ireland.
Newsround takes a look back at his life and explains why he was significant.
Who was Martin McGuinness?
Martin McGuinness was born in Londonderry into a large Catholic family in 1950.
After going to primary school and then college, he began working as a butcher's assistant.
When he was a young man in the late 1960s, there was a lot of conflict in Northern Ireland called the Troubles (read more about it further down).
At this time, Northern Ireland was mostly run by Protestants who were loyal to the UK.
Catholics, a minority in Northern Ireland, held protests because they were finding it difficult to get homes and jobs.
Those protests turned violent and British soldiers were sent in to take control.
Martin McGuinness, a Catholic, became involved with a violent armed group called the Irish Republican Army (IRA) who wanted a united Ireland, totally separate from the UK.
He rose to be an important commander in the IRA, which carried out lots of violent attacks and killed many people.
It even tried to assassinate the UK's prime minister Margaret Thatcher in 1984.
However, he later decided to take a different path and became a politician.
As a politician, he then spent more than 25 years working to bring peace in Northern Ireland.
His journey from violence to politics - and how this journey helped to stop so much conflict in his country - is what makes him so significant to Northern Ireland's history.
Read more about it below.
Martin McGuinness and the history of Northern Ireland
Where did the fighting come from?
The conflict in Northern Ireland dates back to when it became separated from the rest of Ireland in the early 1920s.
Great Britain had ruled Ireland for hundreds of years, but it split off from British rule - leaving Northern Ireland as part of the UK.
When this happened, the population of Northern Ireland was divided in two:
- Unionists, who were happy to remain part of the UK - some of them were also called loyalists (as they were loyal to the British crown)
- Nationalists, who wanted Northern Ireland to be independent from the UK and join the Republic of Ireland - some of them were also called Republicans.
Unionists were mostly Protestant, and Nationalists were mostly Catholic.
When Northern Ireland became separated, its government was mainly Unionist. There were fewer Catholics than Protestants in the province.
Differing views between the two sides caused a lot of tension.
During the 1960s, arguments between the sides turned violent, resulting in a period known as the Troubles.
What were the Troubles?
From the 1970s to the 1990s, armed groups on both sides of the argument were very violent towards each other.
Many people were killed in fighting.
At this time the young Martin McGuinness was an active member of the violent IRA group. He even went to jail because of what he did.
After years of fighting, the 1990s saw a change in Northern Ireland, as the IRA announced it would stop the bombings and shootings.
This gave the Unionists and Republicans the opportunity to try to sort out their problems.
In 1994, Martin McGuinness was named the chief negotiator for Sinn Fein, to have peace talks with the IRA about how to bring the fighting to a stop.
How did peace come about?
In 1997, he became a member of Parliament.
Just one year later, an agreement was signed, which resulted in a new government being formed that would see power being shared between Unionists and Nationalists.
Ten years after becoming an MP - and after being a key figure in peace talks with the IRA - he became deputy first minister of Northern Ireland.
The violence in Northern Ireland didn't stop completely. However, Martin McGuinness publicly spoke out against those who were still being violent, calling them "traitors".
He said: "My war is over. My job as a political leader is to prevent that war and I feel very passionate about it."
In 2012, he shook hands with the Queen when she visited Northern Ireland. This was important because the Queen's cousin Lord Mountbatten was killed by his old group, the IRA.
This was seen as an important symbol of the royal family and Republicans putting their differences to one side.
He stepped down as deputy first minister in January 2017. This is why there have been elections recently in Northern Ireland.
How will he be remembered?
Some people think of Martin McGuinness in a negative way because of the violent things that he and the IRA have done in the past.
But others think of him in a better way, as an important Republican politician who worked very hard to stop the violence and who changed the history of Northern Ireland for the better.