Marian Robinson, mother of former US first lady Michelle Obama, has died aged 86, her daughter said on X on Friday. “My mom Marian Robinson was my rock, always there for whatever I needed,” wrote Obama, whose husband Barack Obama was elected the United States’ first African-American president in 2008. “She was the same steady backstop for our entire family, and we are heartbroken to share she passed away today.” Robinson joined the Obamas and their two daughters Malia and Sasha when they moved into the White House in 2009 and helped take care of her grandchildren during the eight years of Obam…