The article discusses the evolution of mitochondria, emphasizing their bacterial ancestry and the endosymbiont hypothesis. Mitochondria are believed to have originated from α-Proteobacteria, but their evolution has varied significantly across different eukaryotic lineages. The mitochondrial genome has undergone extensive expansion and reduction, with most proteins being encoded in the nucleus through endosymbiotic gene transfer (EGT). Phylogenetic studies support a monophyletic origin of mitochondria, suggesting a single ancestor. However, the specific evolutionary pathway remains controversial, with the archezoan scenario (endosymbiosis with an amitochondrial host) and the symbiogenesis scenario (endosymbiosis with an archaeal host) being proposed. The article also highlights the discovery of mitochondrial-related organelles (MROs), such as hydrogenosomes and mitosomes, which are highly reduced forms of mitochondria. Comparative genomics and proteomics have revealed a mosaic evolutionary origin of the mitochondrial proteome, with a significant proportion of proteins having no clear bacterial or archaeal ancestry. The article concludes by emphasizing the ongoing refinement of our understanding of mitochondrial evolution through continued genomic and proteomic research.The article discusses the evolution of mitochondria, emphasizing their bacterial ancestry and the endosymbiont hypothesis. Mitochondria are believed to have originated from α-Proteobacteria, but their evolution has varied significantly across different eukaryotic lineages. The mitochondrial genome has undergone extensive expansion and reduction, with most proteins being encoded in the nucleus through endosymbiotic gene transfer (EGT). Phylogenetic studies support a monophyletic origin of mitochondria, suggesting a single ancestor. However, the specific evolutionary pathway remains controversial, with the archezoan scenario (endosymbiosis with an amitochondrial host) and the symbiogenesis scenario (endosymbiosis with an archaeal host) being proposed. The article also highlights the discovery of mitochondrial-related organelles (MROs), such as hydrogenosomes and mitosomes, which are highly reduced forms of mitochondria. Comparative genomics and proteomics have revealed a mosaic evolutionary origin of the mitochondrial proteome, with a significant proportion of proteins having no clear bacterial or archaeal ancestry. The article concludes by emphasizing the ongoing refinement of our understanding of mitochondrial evolution through continued genomic and proteomic research.