Short answers, pulled from the story.
Jan Swammerdam first described the red blood cell in the year 1658 while observing the blood of a frog through an early microscope. He became the first human to document these cells, which are now known to be the most abundant cell type in the vertebrate body.
There are roughly 20 to 30 trillion red blood cells circulating in the body at any given time, constituting approximately 84% of all cells in the human body. These cells make up nearly half of the blood's volume and contain approximately 270 million hemoglobin molecules each.
A red blood cell has a functional lifetime of about 100 to 120 days in a healthy individual before it undergoes eryptosis or programmed death. The aging cell changes its plasma membrane and is subsequently phagocytosed by macrophages in the spleen, liver, and lymph nodes.
Karl Landsteiner published his discovery of the three main blood groups A, B, and C in 1901, later renaming group C to O. A year later, Alfred von Decastello and Adriano Sturli identified the fourth blood group AB, laying the foundation for safe blood transfusions.
The oldest intact red blood cells ever discovered were found in Ötzi the Iceman, a natural mummy who died around 3255 BCE, and these cells were discovered in May 2012. This finding highlights the enduring importance of understanding the red blood cell from its microscopic structure to its role in human history.