Animal Companion (5e Feat)
From D&D Wiki
You gain a beast companion that accompanies you on adventures and is trained to fight alongside you. Choose a beast that has a challenge rating equal to or lower than half of your proficiency bonus, rounded down. Add your proficiency bonus to the beast's AC, attack rolls, and damage rolls, as well as to any saving throws and skills it is proficient in. Its hit point maximum equals its normal maximum or six times your hit dice, whichever is higher.
On each of your turns, you can use your bonus action to command the beast provided it can see or hear you. You decide what action the beast will take and where it will move during its next turn, or you can issue a general command, such as to guard or attack a target. If you issue no commands, the beast only defends itself against hostile creatures.
If the beast dies, you can obtain other one by spending 8 hours magically bonding with another beast that isn't hostile to you, either the same type of beast as before or a different one.