The bad one at the beginning of Captain America 3 is Crossbones.

Crossbones was the leader of S.H.I.E.L.D.'s Rapid Response Special Forces in Captain America 2, and was actually HYDRA embedded in S.H.I.E.L.D..

Crossbones has no superpowers, but as a disciple of the Master Impersonator and a character who has fought Captain America many times, his fighting skills are world-class. He excels in street fighting, military combat, and martial arts training.

Despite his tall stature, he possesses disproportionate agility. He is also a skilled pilot; adept with firearms, bows and arrows, and flying daggers, usually armed with a short sword and crossbow, as well as multiple throwing daggers, with spring-loaded daggers hidden in his wrist armor, and a knack for physical and mental torture.

Expanded profile:

Marvel Cinematic Universe Crossbones Appearances

1. Brock Rumlow made his first appearance in the 2014 film Captain America 2. He was the leader of S.H.I.E.L.D.'s Rapid Response Special Forces, but was later revealed to be a member of HYDRA. Rumlow aided Captain America in his mission to root out George Bartok's (Bartok the Jumper) pirate crew and rescue hostages.

When Captain America reveals that Rumlow's team and Pierce are members of HYDRA operating within S.H.I.E.L.D., Rumlow, who arrives in the command room, clashes with Sharon Carter and later engages the Falcon. The out-of-control Sky Mothership crashed into the Triskelion and brought the engagement to an end, also causing Lumlow to suffer severe burns.

2. Brock Rumlow returned as Crossbones in the 2016 movie Captain America 3: Civil War. It was revealed that Captain America and several other Avengers had been tracking Crossbones for six months.

In the movie's opening scene, Crossbones' team of mercenaries storm the Infectious Diseases Institute in Lagos, Nigeria, to seize a biological weapon. While attempting to escape, they are pursued by Captain America, Black Widow and Scarlet Witch, and Falcon. The two sides then engage in a battle at a bazaar, where Crossbones confronts Captain America in hopes of avenging what happened earlier.

Despite using his power-enhancing gloves, Crossbones was defeated and then had his helmet removed, revealing his scarred face. Crossbones finally attempts to kill the captain by detonating his bomb undershirt.

However, the Scarlet Witch briefly restrains the blast and attempts to levitate Crossbones into the air, but the bomb explodes close to a building, killing Crossbones and affecting a number of civilians.

3. Returning via flashback in the 2019 movie Avengers 4: Endgame. During the events that took place in Avengers. With the Battle of New York over, he comes to collect Loki's scepter as part of a team of Hydra agents, but is tricked by the time-traveling Captain America and thus gives the scepter to the Captain.

Baidu Encyclopedia - Crossbones