Leo Anthony Gallagher Jr., known simply as Gallagher, was an iconic American comedian recognized for his prop-based and observational comedic style. Born on July 24, 1946, in Fort Bragg, North Carolina, to a family of Irish and Croatian heritage, Gallagher overcame asthma and pursued a career in comedy after obtaining a chemical engineering degree from the University of South Florida. He gained fame for his unique routine involving the "Sledge-O-Matic," a large mallet with which he smashed various items, particularly watermelons, delighting audiences for over three decades. Despite making appearances on popular TV shows and running for governor in the 2003 California gubernatorial recall election, Gallagher primarily remained a touring comedian, amassing over 3,500 live shows in his career. While his Sledge-O-Matic act and witty wordplay brought him immense success, Gallagher faced criticism for offensive jokes, leading to controversies and mixed reception in later years. Despite enduring serious health issues, Gallagher continued to tour until 2020. His legacy as a pioneering comedian endures, leaving an indelible mark on the world of comedy.

Gallagher and Lyle, the Scottish musical duo, comprised of singer-songwriters Benny Gallagher and Graham Lyle, gained recognition in 1968 when they were signed by the Beatles to write for Apple Records' artists. Their musical style mainly consisted of pop, soft, and folk rock-oriented songs. The duo's breakthrough came with their formation in 1972, releasing their fifth album "Breakaway," which included hit tracks like "Heart on My Sleeve" and "I Wanna Stay with You." Their song "Stay Young" reached No. 1 on the US Country charts when recorded by Don Williams. Throughout their career, Gallagher and Lyle worked with renowned artists such as Paul McCartney, Eric Clapton, and Pete Townshend, and their songs were recorded by a diverse range of artists including Art Garfunkel, Ringo Starr, and Bryan Ferry. After a split in 1980, the duo reunited in 2010, collaborating intermittently as a live act until 2018. Their musical influence and collaborations have left an indelible mark on the industry, making them a celebrated and influential duo in the music world.

The Gallagher index is a statistical measurement used in political science to assess the disproportionality between votes received and seats in a legislature. It calculates the difference between the percentage of votes and the percentage of seats each party obtains in an election, providing a precise score that allows comparison across different electoral systems and elections. Created by Michael Gallagher, the index is also known as the "LSq" index, derived from the sum of squares of residuals used in the method of least squares. It is computed by taking the square root of half the sum of the squares of the differences between the percentages of votes and seats for each political party. The Gallagher index gained attention in Canada in 2016 during efforts to reform the electoral system, with the Special Committee on Electoral Reform recommending its use to minimize distortion between the popular will of the electorate and resultant seat allocations in Parliament. In the 2015 Canadian federal election, the Gallagher index was 12.02, indicating some disproportionality in the election outcome. This index has also been used to assess electoral systems in other countries, such as Australia.

The Gallagher family, also known as Ó Gallchobhair in Irish, has a rich history dating back to the 10th century. They were one of the prominent clans of Cenél Conaill in County Donegal, and held the High Kingship of Ireland during the early medieval period. The family's lineage can be traced back to their progenitor Gallchobhar mac Rorcain, who was the senior-most descendant of Conall Gulban, son of Niall Mór Noigíallach. The O'Gallaghers also held the hereditary Marshal rank of the Kingdom of Tyrconnell, ruled by their kinsmen, the O'Donnells, from the 14th to the early 17th century. The family's origins can be linked to Conall Gulban, who founded the kingdom of Tír Chonaill (Tyrconnell) in the 5th century, encompassing much of present-day County Donegal and surrounding areas. The Gallagher Y chromosome haplogroups can be genetically traced back to a single medieval individual, supporting the legend of Niall Noígiallach. The O'Gallagher clan has its roots in the Irish baronies of Tír Aodha/Tír Hugh and Raphoe in County Donegal, with Ballybeit and Ballynaglack serving as their seats of power. They were anciently chiefs of Cenél