Lucius Heyer is Francon's partner in the firm, and he's basically around for his money and his social connections. He's not much use to anyone, because he's an old dude with health problems. His retirement day is way overdue.
After he has a stroke, Francon and others try to convince Heyer to retire, but he won't. Whether he's being spiteful or just confused in his old age and bad health, we never really know. Keating grows increasingly resentful of Heyer for not clearing out and letting Keating become a partner in the firm. In one the book's most chilling scenes, Keating goes to confront Heyer and ends up shouting at the man, triggering another stroke. Heyer dies soon after, and we discover, along with Keating, that Heyer left Keating a ton of money in his will.
This is another subtle-as-a-sledgehammer Rand moment: the new face of architecture effectively slaughtering the old guard.