Physiologically inactive form is:
Angiotensin I is <1% as potent as Ang II. Ang III and Ang II have qualitatively similar eﬀects; both stimulate aldosterone secretion with equal potency, but Ang III is only 25% and 10% as potent as Ang II in elevating blood pressure and stimulating the adrenal medulla, respectively. Angiotensin III produces the hexapeptide sometimes called angiotensin IV, which is also said to have some activity.
The lungs play an important role in activating angiotensin. The physiologically inactive decapeptide angiotensin I is converted to the pressor, aldosterone-stimulating octapeptide angiotensin II in the pulmonary circulation. Angiotensin III  has about 40% of the pressor activity of angiotensin II, but 100% of the aldosterone-stimulating  activity. Angiotensin  III  is  simply  a  breakdown  product  with  some ​biologic activity. The same is probably true of angiotensin IV, though some researchers have argued that it has unique effects in the brain.
Structure of the amino terminal end of angiotensinogen and angiotensins I, II and III in humans.​
Angiotensin I
Angiotensin II
Angiotensin III
Angiotensin IV