Max is effectively the electronic brain/personality of a research ship - he identifies himself as a Trimaxian Drone Ship, much like the probes NASA launches to photograph distant stars etc. His purpose is to collect data from other planets and return them to his point of origin: Phaelon.
Max is equipped with a faster than light drive of an undisclosed nature and time travel function, allowing him to return samples exactly as found without a second missing in-between abduction and return. This means he does not disturb the environment he came to observe.
Over the course of the movie, Max comes to collect samples from Earth and return them to Phaelon. Along the way, he crashes into an electricity pylon, knocking out his navigational information and disorientating him long enough to be literally picked up by the US government. The information he needs was stored in David Freeman who was abducted by him as a sample in 1978 and had the information implated in the unused area of his brain as an experiment.
Unfortunately, due to the complexities of humans, Max was unwilling to transport David back to his time as he risked killing him, so he replaced him in exactly the same spot he was abducted from, with no memories of it eight years later in 1986. For him the transition was seamless and, due to the warping of time as you approach the speed of light, he hadn't physically aged from 12. Max meanwhile is captured by the US government and subjected to experiments (mainly trying to find the door) and does not attempt to escape as he has no navigation.
Eventually David's unused implated data leads him to Max and in exchange for the information, Max agrees to take him back to his time, 1978, to return to his original parents (not the ones who have been looking for him for eight years). When Max does receive the information he needs, he gets something more — he gains the ability to feel and express emotions, making him more human-like in behavior, but also erratic, stubborn, and argumentative.
- Max was voiced by Paul Reubens (credited as Paul Mall), famous for his childlike persona, "Pee-Wee Herman". Pee-Wee's characteristic laugh is uttered several times by Max after he "contracted" emotions and 1980s knowledge from David. This persona, speaking in an altered pitch similar to Pee-Wee, persists for the rest of the movie, which is a stark contrast to Max's original tone, which is similar to HAL 9000 from Stanley Kubrick's 2001: A Space Odyssey.