Inclusion Criteria:  Age ≥18 years Admitted to the hospital with a diagnosis of acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), or aneurysmal subarachnoid hemorrhage (aSAH) Radiographic confirmatory evidence of: (1) AIS (based on a focal area of restricted diffusion on MRI), (2) non-traumatic ICH (based on evidence of acute parenchymal hemorrhage CT or brain MRI) or (3) non-traumatic acute aSAH (based on evidence of subarachnoid hemorrhage on CT or MRI and evidence of aneurysm on CT angiography, MR angiography, or conventional catheter-based angiography) Able to complete baseline visit in person or by phone within 6 weeks of stroke onset Able to provide informed consent by self or proxy Fluent in English or Spanish prior to stroke onset  Exclusion Criteria:  Documented history of pre-stroke dementia or fails dementia pre-screen Concurrently enrolled into a study that is not approved under the DISCOVERY Co-Enrollment Policy  Unable to complete study protocol (advanced directives such as comfort measures only, or inability to complete the study due to severe medical/behavioral co-morbidities), as determined by physician investigator during screening process  Additional exclusion criteria for Tier 2 participants:  Contraindication to MRI: presence of electrically, magnetically, or mechanically activated implants (such as cardiac pacemakers, cochlear implants, implanted pumps); or metallic clips in the brain  Additional exclusion criteria for Tier 3 participants:  Age <50 years Women who are pregnant or seeking to become pregnant Known to have one of the following genetic conditions which can increase the risk of developing cancer: Cowden disease, Lynch syndrome, hypogammaglobulinemia, Wiskott-Aldrich syndrome, Down's syndrome.