Lou Gehrig's 1939 retirement event at Yankee Stadium in New York City

The transcript recounts Lou Gehrig's emotional farewell at a baseball park, where he received a standing ovation from over 60,000 fans. Gehrig expressed his gratitude and happiness in a brief speech. Two years later, he succumbed to a debilitating illness that ended his career.

What illness did Lou Gehrig succumb to that ended his career?

How did Lou Gehrig's career come to an end?