## 1 Introduction  
Although _Chlorella vulgaris_ (_C. vulgaris_) was described in 1890 by Martinus Beijerinck [1], it has only recently gained substantial attention. This renewed interest is largely due to its diverse chemical composition, extensive bioactive properties, and its potential as a significant protein source for both humans and animals, especially due to the growing global population [2]. _C. vulgaris_ is known for being a rich source of key nutrients, including proteins, vitamins, minerals, and various bioactive compounds, such as carotenoids, chlorophyll, and polysaccharides, all of which contribute to its numerous therapeutic effects [3]. These compounds have been linked to antioxidant, anti-inflammatory, immunomodulatory, immunomodulatory, and detoxifying properties [4]. _C. vulgaris_ has also shown promise in detoxifying heavy metals, enhancing the immune system, and supporting metabolic health, making it a strong candidate for nutraceutical and pharmaceutical applications [5; 6; 7; 8]. In addition, _C. vulgaris_'s high protein content has positioned it as a viable alternative protein source in food products, comparable to other plant-based proteins like soybeans. _C. vulgaris_ contains 43%-to-61% protein by dry weight, depending on growth conditions [9; 10]. Approximately 20% of these proteins are associated with the cell wall, while about 50% are located within the cells. The remaining 30% of proteins are dynamic and may be involved in processes, such as cellular signaling or transport, contributing to various cellular functions as they move in and out of the cell [11]. Additionally, key pigments like chlorophyll have attracted significant interest due to their applications in functional foods, pharmaceuticals, and cosmetics [12]. Chlorophyll has been demonstrated to scavenge free radicals and inhibit lipid peroxidation [13], highlighting its valuable antioxidant properties in health-related products. Beyond its nutritional value, _C. vulgaris_ is recognized for its bioactive compounds, which contribute to its role as a natural antioxidant, immune enhancer, and metabolic regulator [14; 15; 16; 17]. Research on _C. vulgaris_ has specifically investigated its antioxidant and anti-inflammatory activities. Studies suggest that its bioactive compounds, such as phenolic acids, chlorophylls, and carotenoids, may combat oxidative stress and reduce the risk of chronic diseases like cancer, cardiovascular diseases, and diabetes [18; 19]. Regular consumption of fruits, vegetables, seaweed, microalgae, and similar foods can elevate dietary levels of chlorophyll and carotenoids. Among microalgae, _C. vulgaris_ is particularly noteworthy due to its high protein content and abundance of biologically active substances [20]. Additionally, _C. vulgaris_ has demonstrated potential in improving lipid metabolism, enhancing immune function, and detoxifying heavy metals from the body [21; 22]. However, these health benefits can be influenced by factors, such as cultivation methods, environmental conditions, and processing techniques, which impact the stability and potency of its bioactive compounds. This remains an ongoing subject of investigation [23; 24; 25]. For instance, exposure to heat during processing may degrade certain bioactive molecules, reducing their efficacy in nutraceutical applications [26; 27; 28; 29]. With the growing demand for sustainable, functional food sources, _C. vulgaris_ emerges as a promising candidate for nutritional supplementation, medical applications, and animal feed [2]. This manuscript aims to provide a comprehensive assessment of the chemical composition, bioactivities, and diverse applications of _C. vulgaris_ across the food, nutrition, medicine, and animal feed sectors. In doing so, it synthesizes current research from databases such as Google Scholar, PubMed, Scopus, and Web of Science to highlight the health-promoting effects of _C. vulgaris_'s bioactive compounds, including their antioxidant, anti-inflammatory, detoxifying, lipid-lowering, and immune-modulating properties.