**Core Concept**
The patient's presentation is consistent with Cushing's syndrome, a condition caused by excess cortisol production due to an adrenal tumor. The tumor is secreting a hormone that stimulates cortisol release, leading to hypertension, hypokalemia, and suppressed renin activity.

**Why the Correct Answer is Right**
The patient's symptoms and laboratory findings are characteristic of an adrenal tumor secreting aldosterone, a mineralocorticoid hormone. Aldosterone stimulates the kidneys to retain sodium and water, leading to hypertension. It also promotes potassium excretion, resulting in hypokalemia. The suppressed renin activity is a result of negative feedback inhibition by the elevated aldosterone levels. The adrenal tumor is causing an excessive production of aldosterone, leading to Cushing's syndrome due to the mineralocorticoid effect of cortisol on the kidneys.

**Why Each Wrong Option is Incorrect**
* **Option A:** Adrenal tumors secreting catecholamines (e.g., pheochromocytoma) typically present with episodic hypertension, tachycardia, and sweating, not chronic hypertension and hypokalemia.
* **Option B:** Adrenal tumors secreting androgens (e.g., congenital adrenal hyperplasia) typically present with virilization, not hypertension and hypokalemia.
* **Option D:** Adrenal tumors secreting ACTH (e.g., pituitary tumor) typically present with Cushing's disease, not hypertension and hypokalemia.

**Clinical Pearl / High-Yield Fact**
The presence of hypokalemia and suppressed renin activity is a strong clue to the diagnosis of an aldosterone-producing adrenal tumor. This combination is often referred to as the "aldosterone escape phenomenon."

**Correct Answer:** C. Aldosterone.