William Edward Maclagan (5 April 1858 – 10 October 1926) was a Scottish international rugby union forward who played club rugby for London Scottish F.C. Maclagan was one of the longest-serving international rugby players during the early development of the sport, and was awarded 25 caps for Scotland. He played international rugby for thirteen seasons, a Scottish record for sixty years, and led the first official British Isles team on its 1891 tour of South Africa. Maclagan's contributions to the early development of rugby were recognised in 2009 with his induction into the IRB Hall of Fame.