DHT is the most potent androgen, converted from testosterone by the enzyme 5-alpha reductase. It's 3-5x more potent at the androgen receptor than testosterone and plays important roles in libido, mood, body composition, and prostate health. DHT levels tend to be higher with transdermal testosterone (cream/gel) compared to injections.
While DHT is sometimes blamed for hair loss and prostate issues, it's also responsible for many of the benefits men seek from TRT.