Unlike many consumer routers, the WRT54GL was explicitly designed to run Linux-based firmware. The "L" in the model number stands for This allows you to completely replace the stock Linksys firmware with more powerful alternatives.
If you are researching this router for an academic paper or presentation, here is the context regarding why the WRT54GL is historically significant:
The story of the WRT54GL firmware began when Linksys (then owned by Cisco) released the WRT54G. Because the router used Linux-based code, the company was legally required under the GNU General Public License (GPL) to release the source code. This accidental transparency allowed developers to see exactly how the hardware functioned, leading to the birth of custom firmware like DD-WRT and Tomato. Why Custom Firmware Mattered