The penny dreadful was a 19th-century publishing phenomenon. In the 1830s, increasing literacy and improving technology saw a boom in cheap fiction for the working classes. ‘Penny bloods’ was the original name for the booklets that, in the 1860s, were renamed penny dreadfuls and told stories of adventure, initially of pirates and highwaymen, later concentrating on crime and detection. Issued weekly, each ‘number’, or episode, was eight (occasionally 16) pages, with a black-and-white illustration on the top half of the front page. Double columns of text filled the rest, breaking off at the bottom of the final page, even if it was the middle of a sentence.
The bloods were astonishingly successful, creating a vast new readership. Between 1830 and 1850 there were up to 100 publishers of penny-fiction, as well as the many magazines which now wholeheartedly embraced the genre. At first the bloods copied popular cheap fiction’s love of late 18th-century gothic tales, such as The Flying Dutchman. Highwaymen remained a favourite. Gentleman Jack was published over four years, without too much worry for historical accuracy or continuity. Dick Turpin was a great favourite. His story, and especially the time he (supposedly) rode the 200 miles from London to York overnight, was retold endlessly, including in Black Bess; or, The Knight of the Road. Later, after highwaymen and then evil aristocrats fell out of fashion, penny-bloods found even more success with stories of true crimes, especially murders. And if there were no good real-life crimes current, then the bloods invented them. The most successful of them was the story of Sweeney Todd. The ‘Demon Barber’ first appeared in a blood entitled The String of Pearls, which began publication in 1846.
(Adapted from: https://www.bl.uk/romantics-and-victorians/articles/penny-dreadfuls)
The Flying Dutchman: or, The demon ship. 
Viles, Edward. Black Bess: or, The knight of the road: a tale of the good old times. Vol. 3, E. Harrison, [186-]
Clifford, Paul. Gentleman Jack. No. 1-8: or, Life on the road: a romance of interest abounding in hair breadth escapes of the most exciting character. E. Llyod, 1899
Lea, Charlton. Sweeney Todd, the demon barber of Fleet Street. No. 1-48. [s. n.],