Old Gobbo is the father of Launcelot Gobbo, the clown in The Merchant of Venice. Although he only appears in a brief comedic segment in Act II, Scene II, we find out quite a bit about him; his wife (Launcelot's mother) is named Margery, and he owns a "fill-horse", or plow horse, implying that he may be a farmer. His first name is unknown, but it's possible that his son is named after him; Launcelot's name in the quartos and folios is "Launcelet" (diminutive, meaning "little Launce"), and he refers to himself specifically as "young Master Launcelot", so his father could be "old Launcelot" as well as "old Gobbo." (This isn't necessarily the case; it may have been customary to indicate the age of the person spoken of. Launcelot later refers to Bassanio as his "young master", although he could be insultingly contrasting Bassanio with Shylock, the latter being his "old master" in both senses of the word.)
According to Launcelot, Old Gobbo "did something smack, something grow to, he had a kind of taste..." The meaning of these lines is somewhat unclear, but they appear to point to a tendency towards infidelity, and perhaps a penchant for cheating and trickery in other matters. When Old Gobbo shows up, he appears to be rather feeble--he is "sand-blind" (as opposed to stone-blind, which at the time meant "completely blind"--although Launcelot believes that a better term would be "gravel-blind") and doesn't recognize his own son. Launcelot is at first delighted and practices trickery on his father's blindness, but he soon becomes perplexed when his father continues not to recognize him, and then frustrated as he attempts to convince him of his own identity. When Launcelot proves himself to be Gobbo's son by mentioning that "Margery, your wife, is my mother", the two are happily reunited. Old Gobbo is delighted to find that his son has grown an impressive "beard"; according to theater tradition, he has accidentally seized upon Launcelot's long hair, and Launcelot has little or no beard at all.
Launcelot informs his father that he plans on running away from his master, Shylock, unless he can get a position among Bassanio's servants; finding that Old Gobbo has brought a "dish of doves", he encourages him to give them to Bassanio, instead. At this moment Bassanio happens along with several of his servants. Father and son attempt to explain the situation to him, with Launcelot simultaneously encouraging Gobbo to do the talking and interrupting everything he says. Finally, Bassanio tells Launcelot that Shylock has already recommended him as a servant, and tells Old Gobbo to accompany Launcelot to Shylock's house to take his leave. Launcelot walks away with his father, and, although Launcelot recurs, Old Gobbo makes no more appearances in the play.