themes:: The self, identity, physical body, appearance, and how one initiates things. It’s the lens through which the world is experienced, and can manifest as one’s “first impression” to the world, including temperament, demeanor, posture.
The 1st house’s planet ruler naturally becomes the chart ruler. Example: a chart with a 1H Aries is ruled by Mars (in whichever sign Mars is on that chart).
There’s a branding theory slowly increasing in popularity to match one’s brand identity and/or personal style according to one’s rising sign and rising sign ruler. If this is for a work identity, then it’s done in combination with one’s Midhaven (10H) sign and Midhaven sign ruler.
The shadow or mirror of the 1H is 7H, which concerns “the Other,” one’s partnerships, projects and commitments.