Since its discovery by Theodor Escherich in 1885, Escherichia coli has played pivotal roles in microbiology. Initially isolated from the faeces of healthy individuals, E. coli has since become a model organism for bacterial research due to its relative ease of cultivation and genetic malleability. This presentation will explore the historical milestones and contemporary significance of E. coli, particularly its impact on human and animal health with an emphasis on gastrointestinal infections. The versatility of E. coli which enables its existence both as a harmless commensal in the intestines of humans and animals and as a potent pathogen, has made it a fascinating microbe to investigate. Pathogenic varieties, such as enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli and enterohaemorrhagic E. coli (EHEC), are major causative agents of gastrointestinal infections, leading to significant morbidity and mortality worldwide. Yet other biotypes are Shigella “species”, which are serologically-defined, non gas-producing variants of E. coli that are the leading cause of bacillary dysentery. ETEC are prevalent in non-industrialised countries, causing travellers’ diarrhoea and infantile diarrhoea, while EHEC outbreaks resulting in haemorrhagic colitis and the haemolytic uremic syndrome are most common in industrialised nations and often linked to contaminated food sources. E. coli also serves as an important reservoir of genes encoding antimicrobial resistance (AMR). Understanding the pathogenesis, transmission, and prevention of E. coli infections remains a key focus of microbiological research, while the continuing importance of E, coli as a primary and opportunistic pathogen underscores the ongoing efforts to develop effective vaccines, improved diagnostic methods, and public health strategies to mitigate the burden of E. coli-related diseases. The historical and contemporary insights into E. coli enhance our understanding of bacterial pathogenesis in general while informing broader applications in microbiology and medicine.