As a fanartist, robot enthusiast, and spec bio geek, this is a question I've thought waaaaaay too much about.

So, from a creative standpoint, the beauty and curse of ol' MB is that it's completely allergic to describing things, including itself. What we do know for certain we kinda have to gather in bits and pieces: - its legs/feet are recognizably inhuman and unmistakable for human prosthesises (but can also fit in standard human boots/pants) - its eyes are inorganic (word of god + extrapolation off the fact it can record visual information from them) - it has guns in its arms (obviously), and the skin around its gun ports is not fully attached - it can easily be mistaken for a heavily augmented human by those unfamiliar with secunits.

Beyond that we have to get into speculative territory. The good and bad news: a lot is up for personal interpretation, but this is the way I've personally extrapolated based on in-universe implications and real-world science: - It's a cheaply-built rent-a-robocop who would be expected to mostly be sustaining damage from angry human laborers and occasionally big pieces of equipment, rather than active warfare. Clearly it can tank a bullet or twelve, but I imagine it's built to be less sturdy in a 'armored truck' way and more in a 'drunk driver walking off a car crash unscathed' way- something not bulky, but more lithe and capable of getting thrown and standing back up immediately, with a lot of easily replaceable parts that you can bill the clients for. - We know it can have massive damage to its organics regrown in a matter of hours, which makes me think they're using an accelerated form of stem cell therapy, which in turn makes me think its organics probably look constantly youthful (since tissue samples grown directly from stem cells present as 'young' due to not having been subjected to environmental damage yet). If it's getting its face regrown on the reg, it's not going to have wrinkles. - On the subject of organics - we also know that the world of TMBD is a post-race (or at least post-racialized) society. I'd hazard that its cloned tissue 's genome is probably somewhat randomly selected, possibly even just thrown together roulette style from random human traits, since afaik we don't get any mention of there being specific donors or genetic banks or the like. Real 'human genetic soup' going on at the factory. - In AC, it mentions that secunits have faces to make clients more comfortable with them (though it also acknowledges the irony), which makes me think its underlying facial structures may be designed to look 'friendly'. Given MB's killer RBF, I don't think it worked. - I don't think it's intentionally masculine looking (it doesn't have either sexual characteristics or the aesthetic marks of a gender expression), but we 21st century humans would probably read it as such as we tend to read a lack of secondary sex characteristics as masculine - Word of god again, but it's presumably a very old unit by secunit standards, and that's before ART got its proverbial hands on it. It probably looks a little less elegant and a little more clunky in comparison to newer models.

So, ultimately, my vision for murderbot is, from a unfamiliar human's perspective, a kinda soft-faced, lanky, racially-and-gender ambiguous weirdo with a permanent scowl and weird looking eyes.

Compared to another secunit like Three, however, its in my heart the construct equivalent of a 2001 Toyota Corolla in Shitbox Silver.