Lazar was the leader of the humans in suspended animation on the Nerva Beacon. He was nicknamed Noah by the other personnel, after the biblical figure. He had been pair-bonded with Vira for the re-colonisation of Earth.
In 16087, he was woken by Vira. He immediately assumed that the Fourth Doctor, Harry Sullivan and Sarah Jane Smith, who he branded regressives, were responsible for the absence of Dune, who wasn't in the cryogenic chamber with the other humans. He was unwilling to allow the travellers to sully the genetic pool and wanted them killed.
Noah went to the main control room where he found evidence of sabotage. Again, he attributed this to the Doctor. A Wirrn larvae attacked him, leaving its slime on his hand. The infection began to spread throughout his body and his mind became linked to the collective Wirrn hive-mind. He shot Libri with Vira's energy pistol but managed to regain enough control over his own mind to contact Vira and tell her to get off the beacon as she and the humans were in danger. He passed command on to her.
When the Doctor next encountered him, the infection had spread up one side of his body. He told the Time Lord that the Wirrn would soon reach the adult stage. This soon took effect on Noah as he became fully Wirrn - the Swarm Leader. He told the Doctor about the Wirrn's desire to gain technological knowledge, which they could access by using humans as hosts.
Noah attempted to make contact with Vira. The Doctor tried to appeal to his humanity, talking to him about the Earth, but he claimed to have no memory of the planet. He threatened to turn off the oxygen pumps if they did not surrender.
When the Wirrn reached adulthood, Noah led them onto the transport ship of Nerva which was detached from the beacon. It took off into space. Noah contacted Nerva and said goodbye to Vira before the rocket exploded. Because of this the Doctor and Vira instantly realised he had retained his humanity, having not set the rocket stabilisers so that it would be destroyed, taking the swarm with it. (TV: The Ark in Space)