Seán William McLoughlin ( mə-GLOK-lin; born 7 February 1990), better known publicly as jacksepticeye, is an Irish YouTuber whose videos focus on gaming, comedy and vlogging.

Raised in Cloghan, County Offaly in Ireland, McLoughlin played video games from a young age. He started uploading videos to YouTube in December 2012 and his channel grew rapidly in the following years, reaching a million subscribers in 2014 and 10 million by 2016. Throughout 2017, McLoughlin appeared on Disney XD and Irish national television before touring in Europe and the US in 2017 and 2018 for his How Did We Get Here tour and the Game Grumps' Ready Player 3 tour.

In 2018, McLoughlin began streaming exclusive content on Twitch as part of a multi-year deal with Disney Digital Network. He continued to create YouTube videos and appear in live events, including Summer Game Fest in 2020. In 2021, McLoughlin appeared in the film Free Guy starring Ryan Reynolds. The following year, he released a biographical documentary entitled How Did We Get Here? which featured footage from his tour of the same name.

McLoughlin is a co-founder of the clothing brand Cloak with fellow YouTuber Markiplier and the founder and owner of the Top of The Mornin' Coffee company. He is also an active philanthropist, participating in fundraisers that have raised tens of millions for charitable organizations.