Short answers, pulled from the story.
Erik Selvig is portrayed by Stellan Skarsgård across multiple MCU films. Skarsgård signed a five-film deal with Marvel in October 2009 and has appeared in Thor (2011), The Avengers (2012), Thor: The Dark World (2013), Avengers: Age of Ultron (2015), and Thor: Love and Thunder (2022).
Erik Selvig is an astrophysicist, specifically a professor of Theoretical Astrophysics at Culver University. He was born in 1951 in Stockholm, Sweden, and grew up hearing stories about the legends of Asgard.
Under Loki's mental control, Selvig carried the Tesseract to the top of Stark Tower and opened a portal that summoned the Chitauri to invade New York City. After Tony Stark knocked him out, Selvig was freed from the mind control and told Natasha Romanoff that Loki's scepter could close the portal.
Selvig was killed by Thanos during the Blip in 2018. He was brought back to life in 2023 by Bruce Banner, following the events of Avengers: Endgame.
The Cosmic Quest Volume Two: Aftermath is a 2018 tie-in prose novel in which Erik Selvig is the main character. It is set after the events of Avengers: Infinity War, though its depiction of Selvig surviving the Blip was later retconned by Avengers: Endgame.
The experience of being under Loki's control caused Selvig to suffer a mental breakdown in the year following the New York invasion. He had fully recovered by 2015, indicating the breakdown and its aftermath lasted roughly two years.