Thomas Clarkson ought to be at least as famous as William Wilberforce for his part in the abolition of the Slave Trade. The fact that he isn't is largely down to the phenomenal PR job done by Wilberforce's sons after he died. They published a massive five-volume biography of their father which played down the importance of Clarkson. They did eventually apologise to Clarkson, but by then, it was too late!
If Wilberforce was the political arm of the Abolition campaign, Thomas Clarkson was the grass-roots, collecting evidence to support the case and win people round. To do this, Clarkson visited cities all around the UK. He interviewed 20,000 sailors who had worked on the slave ships, and collected all sorts of dreadful items from the ships such as shackles, thumbscrews, and branding irons. This didn't make him at all popular with the slave traders - the Trade was still legal and some people were making a lot of money out of it. Clarkson's activities put him in great personal danger - in Liverpool, some sailors were paid to kill him and he was lucky to escape alive.
Thomas Clarkson painted by Carl Frederick von Breda. He looks a bit serious, don't you think!
Clarkson soon saw that his collection of objects had a powerful effect on people, and made them more likely to listen to him. In addition to the horrific instruments used to restrain and punish the slaves on the ships, he collected examples of high quality craftsmanship made by Africans, such as beautifully woven cloth and leather work. He wanted his European audience to see that the African people being kidnapped were sophisticated, and didn't deserve the terrible treatment meted out on them. You can see pictures of what was in the box Clarkson took round the country with him on the internet here - I think it's really fascinating!
During the course of his mission to collect evidence, and to present his box to the anti-slave trade societies springing up all over the country, Clarkson rode 35,000 miles on horseback. Although the very first Bill put forward to Parliament in 1791 for the Abolition of the Slave Trade was easily defeated by 163 votes to 88, Clarkson and the other abolitionists didn't give up. They continued to work to win round public opinion and put pressure on Parliament. The fact that the Slave Trade was abolished in 1807, and money put aside to pay for the Royal Navy to enforce the new law, was due in no small part to Thomas Clarkson's efforts.
Once the Trade was abolished, he turned his attention to the abolition of slavery itself. And when slavery was finally outlawed in the British colonies in 1833, he shifted his focus to the abolition of slavery in the US. He died at the grand old age of 86, having achieved an enormous amount. He deserves to be celebrated.