Leonard "Lenny" Kruger was the alias of a Byulnian hungry for power. Fed up with the species' laws against extra-planetary travel and recording devices, he kidnapped three children — Myamus, Jecomen and Kappaban — brought them to 20th century Earth on the Pfannkuchen, and set them up as the human pop band the Common Men.
His plan was to harness the power created by their mighty popularity — squashing the Beatles, the band that had inspired his plan — to gain almost infinite power. In the main timeline at least, he was unsuccessful, was apprehended by his own people and was put to trial for his crimes.
Alternate timeline[]
In an alternate timeline, however, his plan worked out rather nicely. Jumping through time with a matter dematerialisation circuit, he teamed up with "schoolgirl" Sadie to make the Common Men the most popular band in the whole planet. With the help of a psychic amplifier, he multiplied the public's obsession for the group to an unnatural high. He had complete mastery over the group through subliminal suggestion.
He then became the band's manager in 1967, gaining even more power over them. He made them famous not just in the United Kingdom, but in the United States and around the globe. When they split up and Mark Carville killed James O'Meara in 1970, he had to restart.
After further manipulation in time, the Common Men got back together, all transformed into their true forms together, and gave Lenny all the power he wanted. He became one of the most powerful men, if not the most powerful, in Mutter's Spiral, and gathered a huge army and a great deal of advanced technology. He then took it all back to the 1950s in space-time vessels, to defeat his greatest enemy, the man who had been the greatest threat to his rise to power: the Fifth Doctor.
The Doctor, however, had other plans. He created a further timeline in which a fake corpse, supposedly that of James, was discovered, and Lenny was said to have murdered him. Teaming with the Doctor, the Common Men confirmed this, and that James had been subsequently replaced by a lookalike. With bad press on him across the Earth, Lenny was severely weakened.
With only a day or two to live, Lenny was given an offer from the Doctor. Since he would otherwise die, Lenny complied, and gave the Doctor the code to unlock the time lock that he had placed on the year 1957. The Doctor was able to undo the damage Lenny had done, thus restoring the original timeline. After this, Lenny did not even remember the great feats he'd accomplished in the alternate timeline, and was once again put on trial by the Byulnians. (AUDIO: 1963: Fanfare for the Common Men)