A Study to Evaluate Efficacy and Safety of MK-8690 in Participants With Moderately to Severely Active Ulcerative Colitis (MK-8690-002)

The main inclusion criteria include but are not limited to the following: * Has had ulcerative colitis (UC) (from onset of symptoms) for at least 3 months before Randomization * Has moderately to severely active UC * Has a weight ≥40 kg * Satisfies at least 1 of the criteria: Has had an inadequate response or loss of response to 1 or more protocol-specified treatments; protocol specified corticosteroid dependence; has been intolerant to 1 or more protocol-specified UC treatments * Is on treatment with any protocol-specified drugs during the study and meets drug stabilization requirements, as applicable The main exclusion criteria include but are not limited to the following: * Has a diagnosis of Crohn's Disease (CD) or indeterminate colitis (inflammatory bowel disease (IBD)-undefined) or other types of colitis or enteritis that may confound efficacy assessment * Has a current diagnosis of fulminant colitis and/or toxic megacolon * Has UC limited to the rectum * Has a current or impending need for colostomy or ileostomy * Has had a total proctocolectomy or partial colectomy * Has UC exacerbation requiring hospitalization within 2 weeks before Screening * Has any active infection as specified in the protocol * Is known to be infected with hepatitis B virus (HBV), hepatitis C virus (HCV), or human immunodeficiency virus (HIV) * Has evidence of active tuberculosis (TB) or meets TB exclusionary parameters * Has a history of cancer (except fully treated nonmelanoma skin cell cancers or cervical carcinoma in situ after complete surgical removal) and is disease free for \<5 years before Randomization or has a history of colorectal cancer at any time * Has prior or current evidence of definite colonic dysplasia except for low-grade dysplasia that has been completely removed * Has had major surgery within 3 months before Screening or has a major surgery (ie, surgical procedure requiring general anesthesia) planned during the study * Has received protocol-specified prohibited medications