Maxwell Collins was the child of Lloyd and Devina Collins and the younger brother of Jess Collins. He liked superhero comic books and aliens. When the Twelfth Doctor was trapped in 1972 without a working TARDIS, he lived with the Collins and became best friends with Maxwell. (COMIC: Moving In)
On a school day in 1972, Maxwell had Sugar Joy! cereal for breakfast. He told his mum to get more Sugar Joy! because each box came with a free alien toy. Six minutes later he took a school bus to school. That day, his sister, father, and mother had an adventure with the Twelfth Doctor which ended with the Doctor's TARDIS overloading itself to purge London of an alien disease.
Two days later, Devina Collins invited the Doctor to live with them because he didn't have anywhere else to go. Maxwell greeted the Doctor and pulled him inside the Collins household when he tried to refuse Devina's hospitality. (COMIC: The Pestilent Heart)
Three days after that, Maxwell encountered the Doctor resting his head against the TARDIS in the backyard. The Doctor told Maxwell he was trying to psychically encourage the TARDIS to reweave its outer plasmic shell. Maxwell joined in, but quickly became bored and asked the Doctor who would win in a fight: Captain America or Batman. The Doctor argued that Captain America would win, but Maxwell was certain Batman would. Their conversation reached an end when Jess walked into the backyard. After Maxwell went back inside, Jess commented that she thought the Doctor had made a new best friend. (COMIC: Moving In)
About a day later, Maxwell came with the Doctor and Jess to the National Gallery. While the Doctor and Jess enjoyed the art, Maxwell was unimpressed; at one point he said that John Constable was "no Jack Kirby". The visit to the gallery was interrupted when a small monkey-like alien was released by alien hunters from Kolothos (where hunting was outlawed) and the hunters sent hounds to chase it into the gallery. The Doctor, Jess, and Maxwell followed the chase outside into Trafalgar Square where they encountered the hunters. The Doctor tried to stop them from killing the monkey-like alien and managed to knock out Broteas, but Broteas' wife Skadi still managed to kill the alien. With their hunt over, Skadi and her son Tarquel took Jess and Maxwell aboard their ship, while Broteas was arrested on Earth.
Because of Tarquel's disgust with the hunting and killing his parents did, Maxwell worked together with Tarquel and tricked Skadi into dropping her weapon when Maxwell pretended to threaten her son. After DCI Jack Hayes arrested Skadi, Tarquel then took Skadi and Broteas back to Kolothos to face justice for their crimes. (COMIC: Bloodsport)
On Christmas Eve, Maxwell asked Lloyd if he was still getting a bike for Christmas. On Christmas morning, during a breakfast Devina put on for the whole street, Maxwell rode his new bike in the garden. (COMIC: Be Forgot)
In 1973, Jess wanted to join Hayes and the Doctor at the station when he was invited to come down, but Hayes insisted only the Doctor could come. Later, the Collins family were knocked out by Katya Dabrowski and her men, and taken to an apartment in central London. They were greeted by the Master, who told them the Doctor was a threat to them and a powerful and deceitful alien. Ensuring the Collins family that the Doctor would never hurt them again, the Master used the artron energy in their body as a means of opening a portal to a time locked dimension, which they were also sent to. Jess, Devina and Lloyd were separated from Maxwell. Maxwell was aged several years by a small tornado. After spotting his father, Maxwell ran after Lloyd and watched as Lloyd was aged to death by a group of alien creatures. A being called Kiadine, who the Time Lords had imprisoned on this world, reversed what had happened to Lloyd. The Master found Kiadine, and was offered his temporal powers, and the Doctor and the Master fought with each other over the power of the chronon storm, when the Collins family pulled the Doctor back, standing together against the Master. The Master attacked them, and this blast was repelled with the same artron energy in the bodies of the Collins family that had brought the Master to the dimension. The temporal effects on Jess and Maxwell were also reversed. The Master survived this attack and left, and with no-one left to keep time in check, the Doctor and the Collins family evacuated. After Gabriel's funeral, the Doctor said goodbye to the Collins family and left in a fully repaired TARDIS, believing he had outstayed his welcome. (COMIC: Doorway to Hell)