The character of Dick Solomon is played by John Lithgow. In this interview, he discusses how he came to be cast in 3rd Rock and the experience of playing the role of Dick Solomon:
Dick is the High Commander and, for the purpose of the mission, he takes a job as a physics professor at Pendleton University. He is in effect the family breadwinner, which reinforces his position as High Commander.
He poses as the head of the family with Sally and Harry taking the role brother and sister respectively, while Tommy passes (just about) as his teenage son. Initially he tells friends and colleagues that his wife is dead, but this causes complications later when the Big Giant Head chooses to send him a 'wife' (his niece, played by Roseanne Barr - see Fun with Dick and Janet) to keep an eye on him.
Through his job at the university, Dick shares an office with Dr Mary Albright. She lectures in anthropology and while they never really hit it off professionally, their relationship does quickly become personal. As well as sharing an office they also share a secretary - Nina Campbell.
As a teacher Dick proves quite lousy but because the subject is physics nobody seems to notice, not least his students, who are mostly happy to assume that it is down to their lack of comprehension - which it is. Although they resent his manner and methods they also seem reconciled to it, largely because they are grateful just to be at college, even if it's a second-rate institution. It is yet another example of 'the emperor's new clothes' syndrome, which allows the aliens to pass as 'human'.
Dick is obsessed with Mary. Having come to Earth with the intent of studying human beings Dick soon replaces this objective by choosing to study one human being in particular, almost to the exclusion of all others. In actual fact it is because of Mary that the mission is prolonged for six years. Initially it would seem that the unearthly visitation was a routine one, only intended to last a couple of days, or weeks at the most.
Despite this, it is frequently suggested by the other aliens that Dick's infatuation with Mary is actually jeopardising the mission. On separate occasions it causes his recall to the home planet; his temporary demotion from position of High Commander; all sorts of friction within the camp. It also earns the ire of the Big Giant Head who takes a disliking to a href="https://sites.google.com/site/thirdrockfromthesunfansite/the-show/the-characters/the-humans/mary-albright">Mary. Dick later discovers the Big Giant Head is his father and the apparent dislike is more a case of paternal disapproval.
Despite, or even because of, Dick's devotion he proves seriously deficient in the boyfriend stakes. The rocky relationship he endures with Mary is largely his own doing. He uses her to dump his own emotional baggage and it is only because Mary herself is insecure that she allows it, and accepts it, never suspecting the unearthly cause of Dick's behaviour. It is Mary who is first to observe that Dick 'acts like he is learning everything for the first time.'
All told, Dick is loud, pompous, arrogant, utterly self-absorbed, an egotistical brute; yet we like him because he really does exult in each and every aspect of the human experience. To him it is almost an addiction. He loves being centre of attention; hates been left out of any activity that is going on around him. Alone among the aliens, Dick comes closest to ditching his alien being in favour of a human one; threatening to do just that on one or two occasions.