A Study of LY3844583 in Healthy Participants and Participants With Atopic Dermatitis

Inclusion Criteria: * Healthy participants (Parts A and B): * Are male or female not of childbearing potential * inclusion of healthy Japanese participants, the participant must be first-generation Japanese, defined as the participant's biological parents and all of the participant's biological grandparents must be of exclusive Japanese descent, and must have been born in Japan. * inclusion of healthy Chinse participants, the participant must be at a minimum, third-generation Chinese, defined as all 4 of the participants' biological grandparents must be of exclusive Chinese descent and born in China. * Must have a body mass index of 18.0 to 32.0 kilograms per meter squared (kg/m²), inclusive. For healthy Japanese participants, have a body mass index of 18.0 to 28.0 kg/m², inclusive, and a body weight of 50 kg to 85 kg, inclusive. * Atopic dermatitis participants (Part C): * Must have a body mass index of 18.0 to 45.0 kg/m², inclusive * Are male or female participants including those of child bearing potential * Must have a diagnosis of AD for at least 12 months with either poor response to topical treatments or inability to use topical treatments * Must agree to use moisturizer daily throughout the treatment period Exclusion Criteria: * All participants: * Have or used to have health problems or laboratory test results or electrocardiogram (ECG) readings that, in the opinion of the doctor, could make it unsafe to participate, or could interfere with understanding the results of the study * Have active or latent tuberculosis * Have had any cancer within the past 5 years. Exceptions: successfully treated basal cell skin carcinoma or squamous cell skin carcinoma, with no evidence of recurrence or metastatic disease within the 3 years prior to baseline * Have one of the following viral infections: hepatitis B virus, hepatitis C virus or human immunodeficiency virus. * Have received treatment with biologic agents (such as monoclonal antibodies, including marketed drugs) within 30 days or 5 half-lives (whichever is longer) prior to dosing * Must not have previously completed a clinical trial with a molecule targeting interleukin-33 and/or the interleukin-33 receptor (ST2) * Are currently participating in or completed a clinical trial within the last 30 days * Have received a vaccine containing a live (attenuated) virus within 28 days of screening or intend to receive during the course of the study * Atopic dermatitis participants: * Must not have received certain topical medications for AD within 2 weeks prior to randomization * Must not have received certain oral medications for AD or received phototherapy within 4 weeks prior to randomization * Must not have received any antibody-based biologic agents (marketed or investigational) within 5 half lives (t1/2) of the drug prior to randomization * Must not have received intravenous, intramuscular, or intra-articular steroids in the past 6 weeks prior to randomization