Ask any Londoner what the statue in Piccadilly Circus is and they'll tell you: it's Eros. The winged boy set to shoot an arrow at an unsuspecting passer-by is the god of love.

Only it isn't. It's actually a representation of Eros' twin brother Anteros, the god of selfless love, rather than erotic, and it was made in homage to Anthony Ashley-Cooper, the seventh Earl of Shaftesbury, who died on October 1, 1885.

Shaftesbury was an evangelical Christian and social reformer, an aristocrat who spent his life working on behalf of those who had nothing. The legislation he steered through Parliament improved the lives of millions. One biographer, Georgina Battiscombe, wrote: "No man has ever done more to lessen the extent of human misery or to add to the sum total of human happiness" – an astonishing claim that becomes more astonishing when you realise that it's absolutely true.

Shaftesbury was a lonely and unhappy child, neglected by his parents and packed off to a boarding school which he hated: "The place was bad, wicked, filthy; and the treatment was starvation and cruelty," he wrote later. His only solace was his Christian housekeeper, Maria Millis, and his sisters, who provided him with the love that was otherwise lacking.

He went to Harrow School, later telling of how on Harrow Hill, he witnessed drunken men carrying the coffin of a pauper child, with no one to mourn the death. He resolved then to devote his life to "pleading the cause of the poor and friendless".

He entered Parliament in 1826 and took up the cause of "lunatics", who were confined to madhouses in appalling conditions. In one, patients were chained up, slept naked on straw, and relieved themselves in their beds. They were left chained over the weekend, after which the accumulated excrement was cleared and they were washed down in freezing cold water. Acts to relieve the worst abuses were passed the following year, but it took decades longer to secure a humane regime. In 1845 Shaftesbury described the case of a Welsh girl, Mary Jones, who had for more than a decade been locked in a tiny loft with little air and no light. The room was so small she could only squat in a bent position and she had become deformed.

Shaftesbury also worked tirelessly at reforming the factories that powered Britain's industrial revolution. Conditions were often appalling – Friedrich Engels wrote The Condition of the Working Class in England in 1845, radicalised by the abuses he saw there. Shaftsbury sponsored a series of bills aimed at reducing the hours worked by children, which were fiercely resisted by Conservatives and libertarians. The Ten Hours Act, which reduced the working hours of women and young people to 10 hours a day, was finally passed in 1847.

Another of his causes was the employment of women and children underground in mines and collieries. In 1838 an overflowing stream at Huskar Colliery in Barnsley killed 26 children. The accident led to a Royal Commission led by Shaftesbury, who exposed the horrific conditions under which they worked. Children as young as five were employed underground opening and closing ventilation shafts before graduating to pushing coal tubs.

Another cause he took up was the use – or abuse – of climbing boys to clean Britain's chimneys, a story fictionalised by another reformer, Charles Kingsley, in his classic The Water Babies. Many of these boys had been sold into the trade by their parents. As well as risking burns and suffocation, many contracted cancer of the scrotum. It took Shaftesbury more than 30 years to stamp out the practice.

Shaftesbury was driven by his evangelical Christian faith, which also saw him act as one of the earliest advocates for Christian Zionism in Britain. He was the first senior British politician to propose the resettlement of Jews in Palestine, writing in his diary in 1853, "There is a country without a nation; and God now in his wisdom and mercy, directs us to a nation without a country."

He was a leading evangelical statesman, working with the Church Missionary Society, the Religious Tract Society, the British and Foreign Bible Society and the Church Pastoral Aid Society. He was not bothered by denominational labels, working closely with the Baptist preacher Charles Haddon Spurgeon and presiding over his fiftieth birthday celebrations.

His guiding principle was expressed in this line: "By everything true, everything holy, you are your brother's keeper."

During his lifetime he became known as "the poor man's earl". His funeral service was held in Westminster Abbey on October 8, 1885, and the streets were thronged with poor people who waited for hours in the rain to see his coffin as it passed by.

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