7. The Sensorites

After the death defying escape from the Aztecs last episode, the Doctor and crew journey to the far future where they meet the alien race The Sensorites. This is the first time the series presents a fully realized humanoid alien species. While the Daleks didn't look human at all and the Thals looked like perfect humans, the Sensorites looked alien. We are quickly introduced to their culture, their planet, their morality and motivations. Within the course of these 6 episodes, we see the spectrum of morality in them from good and benevolent to back stabbing and evil.

In looking at the overall arch of the first season, this story wonderfully presents three dimensional characters for our cast to act with and against. Too often, aliens are played as 2-dimensional cardboard cut-outs (see The Daleks). While the Sensorites do look similar to each other, their individual personalities do emerge from behind the masks to portray a race not to dissimilar to ourselves.

While our TARDIS crew has been yo-yo-ing through time and space, bouncing between the past and the future, each story has presented something different. Again, this story sets the bar for all stories to come with an alien race. Paradoxically, these non-humans show what is most human about us.

en.wikipedia.org/wiki/The_Sensorites

Next episode: The Reign of Terror!