Youth of color are severely underrepresented in STEM which is can be attributed to low socioeconomic status, lack of representation, varying levels of racism faced within different institutions and systems. Without proper support and representation, youth of color can begin to feel that STEM is not a field they identify with or feel they belong. However, Informal STEM programs have been found to be sites of non-traditional STEM learning that support youth of color. This dissertation, based on a three-year study within a local Boys and Girls Club in North Carolina, describes how an informal STEM educator's politicized care pedagogical practice supports Black youth to reauthor their rightful presence in STEM. Using a participatory design-based research approach, I explore how critical relationality that focuses on the integration of youth voice and interest supports youth to develop their STEM-related onto-epistemologies. The findings of this dissertation indicate that the role of the informal STEM educator has a significant impact on how youth perceive themselves in STEM. This is presented through a multiple case study that focuses on how two Black boys co-created learning opportunities in coding, how informal STEM programs can serve as a Black educational space (a socio-spatial imaginary rooted in anti-Blackness), and a critical autoethnography that looks at what it means to be an informal STEM educator within a community-based setting. Through these findings I surface the criticality for informal STEM educators to have a relationship and develop community with the youth they work with. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]