This interactive visualization displays the religious composition of the 20 most populous countries using stacked horizontal bars, where each bar segment represents the population adhering to a particular faith. It renders with SVG and includes a color legend that, when hovered, filters and highlights bars from a single religion while dimming the rest. Built with D3.js (v3.5.5), the code uses `d3.layout.stack` for stacking, `d3.svg.axis` for axes, and `d3.legend.color` for the interactive legend. Population values are formatted with a custom SI formatter that abbreviates billions as "B," and a tooltip shows the exact count on hover.