is he involved in queer activism?
Yes -  LGBT rights. He is co-founder of Stonewall, an LGBT rights lobby group in the United Kingdom
Ian McKellen
McKellen has continued to be very active in LGBT rights efforts. In a statement on his website regarding his activism, the actor commented that:
McKellen is a co-founder of Stonewall, an LGBT rights lobby group in the United Kingdom, named after the Stonewall riots. McKellen is also patron of LGBT History Month, Pride London, Oxford Pride, GAY-GLOS, LGBT Foundation, and FFLAG where he appears in their video "Parents Talking"
who plays gandolf in lord of the rings Sir Ian Murray McKellen what was his debut movie? A Touch of Love can you name some of the most acclaimed stage productions he has acted in? A Scent of Flowers, Macbeth, Othello
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Ian McKellen [SEP] LGBT rights campaigning
Section 28 was, however, enacted and remained on the statute books until 2000 in Scotland and 2003 in England and Wales. Section 28 never applied in Northern Ireland. In 2003, during an appearance on "Have I Got News For You", McKellen claimed when he visited Michael Howard, then Environment Secretary (responsible for local government), in 1988 to lobby against Section 28, Howard refused to change his position but did ask him to leave an autograph for his children. McKellen agreed, but wrote, "Fuck off, I'm gay." McKellen described Howard's junior ministers, Conservatives David Wilshire and Dame Jill Knight, who were the architects of Section 28, as the 'ugly sisters' of a political pantomime.