The friendly, bearded face of Caroll Spinney may not be one you recognize immediately. But if you have watched TV at any point in the past 50 years or so, you are almost certainly familiar with his work. Since 1969, he has played the parts of the gentle, inquisitive Big Bird and the lovably disgruntled Oscar the Grouch on “Sesame Street,” the long-running children’s program.

This Thursday, as he so often has, Spinney, 84, plans to travel to the studios in Astoria, Queens, where “Sesame Street” is produced, and record some voices for his colorful alter egos.

Then he will retire from the program: His roles will be passed on to new performers and his remarkable half-century run, in which he has embodied two of the most beloved characters on television, will come to an end.

Sesame Workshop, the nonprofit education organization that produces “Sesame Street,” did not have a precise figure for the number of episodes Spinney has appeared in, but a spokeswoman said the number was likely thousands of the more than 4,400 episodes that have been created.